125876 + Interview Questions in General QA Page 156 InterviewSolution

7751.	When two bodies move uniformly towards each other, the distance between them diminishes by 16 m every 10s. If the bodies move with vlocitics of the same magnitude and in the same direction as before, the distance between them will increase by 3m every 5s. What is velocity of each body?
Answer» Let v_A and v_Bbe the velocities of the two bodies A and B. When two bodies are moving towards each other: Relative velocity of body A w.r.t.B. v = v_A -(-v_B) = v_A + v_B Since, distance diminishes by m. every 10 s. v = 16/10 = 1.6 ms^-1. or, v_A + v_B = 1.6 .....(i) When two bodies move in the same direction: Relative velocity of body A w.r.t.B. v = v_A - v_B. Since, distance increase by 3m every 5s, v' = 3/5 = 0.6 ms^-1 or, v_A - v_B = 0.6......(ii) On solving the equations (i) and (ii), we get v_A = 1.1 ms^-1 and v_B = 0.5 ms^-1.

7751.

When two bodies move uniformly towards each other, the distance between them diminishes by 16 m every 10s. If the bodies move with vlocitics of the same magnitude and in the same direction as before, the distance between them will increase by 3m every 5s. What is velocity of each body?

Answer»

Let v_A and v_Bbe the velocities of the two bodies A and B.

When two bodies are moving towards each other: Relative velocity of body A w.r.t.B.

v = v_A -(-v_B) = v_A + v_B

Since, distance diminishes by m. every 10 s.

v = 16/10 = 1.6 ms^-1.

or, v_A + v_B = 1.6 .....(i)

When two bodies move in the same direction: Relative velocity of body A w.r.t.B.

v = v_A - v_B.

Since, distance increase by 3m every 5s,

v' = 3/5 = 0.6 ms^-1

or, v_A - v_B = 0.6......(ii)

On solving the equations (i) and (ii), we get

v_A = 1.1 ms^-1 and v_B = 0.5 ms^-1.

Discussion

7752.	Is the time variation of position shown in the Fig. alongside, observed in nature?
Answer» No,since with increase of position x, time first increases and then decreases, which is not possible.

Discussion

7753.	Figure shows a displacements time graph. Comment on the sign of velocities at point P, Q, R, S and T.
Answer» Velocity at P and T is positive Velocity at Q and S is zero Velocity at R is negative

7753.

Figure shows a displacements time graph. Comment on the sign of velocities at point P, Q, R, S and T.

Answer»

Velocity at P and T is positive

Velocity at Q and S is zero

Velocity at R is negative

Discussion

7754.	Velocity-time plot of two particles make angles of 60º and 30º with the axis on which time is plotted. What is the ratio of their acceleration?
Answer» Acceleration is given by the slope of velocity-time graph of an object. Ratio of Acceleration = \(\frac{Acceleration\, of\, Partile\, I}{Acceleration \,of\, Partile\, II}\) \(\frac{tan\,60^o}{tan \,30^o}=\frac{\sqrt 3}{\frac{1}{\sqrt 3}}\) = 3

7754.

Velocity-time plot of two particles make angles of 60º and 30º with the axis on which time is plotted. What is the ratio of their acceleration?

Answer»

Acceleration is given by the slope of velocity-time graph of an object.

Ratio of Acceleration = \(\frac{Acceleration\, of\, Partile\, I}{Acceleration \,of\, Partile\, II}\)

\(\frac{tan\,60^o}{tan \,30^o}=\frac{\sqrt 3}{\frac{1}{\sqrt 3}}\) = 3

Discussion

7755.	When is the relative velocity of two bodies maximum?
Answer» Relative velocity of two bodies is maximum when they are moving in opposite directions.

Discussion

7756.	A police van moving on a highway with a speed of 30 kmh-1 fires a bullet at thief's car speeding away in the same direction with a what speed of 192 km/hr. If the zuzzle speed of the bullet is 150 ms-1, with what speed does the bullet hit the thief,s car?[Note: obtain that speed which is relevant for damaging the thief's car]
Answer» Speed of the police van = 30 kmh^-1 = 5 x 5/3 ms^-1 = 25/3 ms^-1 Speed of thief's car = 192 kmh^-1 = 160/3 The relative speed of thief's car with respect to police van = (160/3- 25/3) ms^-1 = 45 ms^-1 Speed of bullet = 150 ms^-1 The speed with which bullet hit the thief's car = (150 - 45) ms^-1 = 105 ms^-1.

7756.

A police van moving on a highway with a speed of 30 kmh-1 fires a bullet at thief's car speeding away in the same direction with a what speed of 192 km/hr. If the zuzzle speed of the bullet is 150 ms-1, with what speed does the bullet hit the thief,s car?[Note: obtain that speed which is relevant for damaging the thief's car]

Answer»

Speed of the police van

= 30 kmh^-1 = 5 x 5/3 ms^-1

= 25/3 ms^-1

Speed of thief's car

= 192 kmh^-1 = 160/3

The relative speed of thief's car with respect to police van

= (160/3- 25/3) ms^-1 = 45 ms^-1

Speed of bullet = 150 ms^-1

The speed with which bullet hit the thief's car

= (150 - 45) ms^-1 = 105 ms^-1.

Discussion

7757.	The (x -t) graph of a moving particle is shown in the figure below. Comment on the signs of the velocities at the points C,D,E and F.
Answer» The slope of the tangent of (x -t) graph at a point gives the velocity of the body at the point. (i) At C, the velocity is + ve. The tangent to the (x -t) graph at C makes an acute angle with the time axis. Therefore, the shape and hence velocity is + ve. (ii) At D, the velocity is zero. (iii) At E, the velocity is -ve. (iv) At F, the velocity is +ve.

7757.

The (x -t) graph of a moving particle is shown in the figure below. Comment on the signs of the velocities at the points C,D,E and F.

Answer»

The slope of the tangent of (x -t) graph at a point gives the velocity of the body at the point.

(i) At C, the velocity is + ve. The tangent to the (x -t) graph at C makes an acute angle with the time axis. Therefore, the shape and hence velocity is + ve.

(ii) At D, the velocity is zero.

(iii) At E, the velocity is -ve.

(iv) At F, the velocity is +ve.

Discussion

7758.	Two balls have same size but one is dense. When released simultaneously from same height which ball will reach the ground first?
Answer» Retardation (a) of the denser ball due to air resistance is less so (g - a) is more for the denser ball. Thus, denser ball would reach ground first.

Discussion

7759.	Two balls of different masses are thrown vertically upward with same initial speed. Which one will rise to a greater height?
Answer» Both the balls will rise to a greater height.

Discussion

7760.	Write the characteristics of displacement?
Answer» (1) It is a vector quantity having both magnitude and direction. (2) Displacement of a given body can be positive, negative or zero.

7760.

Write the characteristics of displacement?

Answer»

(1) It is a vector quantity having both magnitude and direction.

(2) Displacement of a given body can be positive, negative or zero.

Discussion

7761.	Look at the graphs (a) to (d) (Fig.) carefully and state, with reasons, which of these cannot possibly represent onedimensional motion of a particle.
Answer» (a) From the graph, we see that for certain instants of time, the particle has 2 positions, which is not possible. Hence this graph cannot possibly represent one-dimensional motion of a particle. (b) From the graph, we see that for certain instants of time, the particle has 2 velocities, which is not possible. Hence this graph cannot possibly represent one-dimensional motion of a particle. (c) From the graph, we see that for some instants of time, the particle has negative speed. But speed is always a non-negative quantity. Hence this graph cannot possibly represent one-dimensional motion of a particle. (d) From the graph, we see that for a time interval the total path length is decreasing. But total path length is always a nondecreasing quantity. Hence this graph cannot possibly represent one-dimensional motion of a particle.

7761.

Look at the graphs (a) to (d) (Fig.) carefully and state, with reasons, which of these cannot possibly represent onedimensional motion of a particle.

Answer»

(a) From the graph, we see that for certain instants of time, the particle has 2 positions, which is not possible. Hence this graph cannot possibly represent one-dimensional motion of a particle.

(b) From the graph, we see that for certain instants of time, the particle has 2 velocities, which is not possible. Hence this graph cannot possibly represent one-dimensional motion of a particle.

(c) From the graph, we see that for some instants of time, the particle has negative speed. But speed is always a non-negative quantity. Hence this graph cannot possibly represent one-dimensional motion of a particle.

(d) From the graph, we see that for a time interval the total path length is decreasing. But total path length is always a nondecreasing quantity. Hence this graph cannot possibly represent one-dimensional motion of a particle.

Discussion

7762.	An automobile moving with a uniform velocity of 500 ms-1 is brought to rest in travelling a distance of 5m. What is the acceleration produced by the brakes?
Answer» Initial velocity of the car, u = 500 ms^-1 Final velocity of the car v = 0 Let a be the acceleration of the car. Then using the relation. v² = u²+ 2aS 0² = 500² + 2a × 5 a = -500²/10 = – 25 × 10³ms^-2.

7762.

An automobile moving with a uniform velocity of 500 ms-1 is brought to rest in travelling a distance of 5m. What is the acceleration produced by the brakes?

Answer»

Initial velocity of the car, u = 500 ms^-1

Final velocity of the car v = 0

Let a be the acceleration of the car. Then using the relation.

v² = u²+ 2aS

0² = 500² + 2a × 5

a = -500²/10 = – 25 × 10³ms^-2.

Discussion

7763.	Look at the graphs (a) to (d) (Fig. 3.20) carefully and state, with reasons, which of these cannot possibly represent one-dimensional motion of a particle.
Answer» The given x-t graph, shown in (a), does not represent one-dimensional motion of the particle. This is because a particle cannot have two positions at the same instant of time. The given v-t graph, shown in (b), does not represent one-dimensional motion of the particle. This is because a particle can never have two values of velocity at the same instant of time. The given v-t graph, shown in (c), does not represent one-dimensional motion of the particle. This is because speed being a scalar quantity cannot be negative. The given v-t graph, shown in (d), does not represent one-dimensional motion of the particle. This is because the total path length travelled by the particle cannot decrease with time.

7763.

Look at the graphs (a) to (d) (Fig. 3.20) carefully and state, with reasons, which of these cannot possibly represent one-dimensional motion of a particle.

Answer»

The given x-t graph, shown in (a), does not represent one-dimensional motion of the particle. This is because a particle cannot have two positions at the same instant of time.

The given v-t graph, shown in (b), does not represent one-dimensional motion of the particle. This is because a particle can never have two values of velocity at the same instant of time.

The given v-t graph, shown in (c), does not represent one-dimensional motion of the particle. This is because speed being a scalar quantity cannot be negative.

The given v-t graph, shown in (d), does not represent one-dimensional motion of the particle. This is because the total path length travelled by the particle cannot decrease with time.

Discussion

7764.	A police van moving on a highway with a speed of 30 km h–1 fires a bullet at a thief’s car speeding away in the same direction with a speed of 192 km h–1 . If the muzzle speed of the bullet is 150 m s–1 , with what speed does the bullet hit the thief’s car? (Note: Obtain that speed which is relevant for damaging the thief’s car).
Answer» Speed of the police van, vp = 30 km/h = 8.33 m/s Muzzle speed of the bullet, vb = 150 m/s Speed of the thief’s car, vt = 192 km/h = 53.33 m/s Since the bullet is fired from a moving van, its resultant speed can be obtained as: = 150 + 8.33 = 158.33 m/s Since both the vehicles are moving in the same direction, the velocity with which the bullet hits the thief’s car can be obtained as: v_bt = v_b – v_t = 158.33 – 53.33 = 105 m/s

7764.

A police van moving on a highway with a speed of 30 km h–1 fires a bullet at a thief’s car speeding away in the same direction with a speed of 192 km h–1 . If the muzzle speed of the bullet is 150 m s–1 , with what speed does the bullet hit the thief’s car? (Note: Obtain that speed which is relevant for damaging the thief’s car).

Answer»

Speed of the police van, vp = 30 km/h = 8.33 m/s

Muzzle speed of the bullet, vb = 150 m/s

Speed of the thief’s car, vt = 192 km/h = 53.33 m/s

Since the bullet is fired from a moving van, its resultant speed can be obtained as: = 150 + 8.33 = 158.33 m/s

Since both the vehicles are moving in the same direction, the velocity with which the bullet hits the thief’s car can be obtained as: v_bt = v_b – v_t = 158.33 – 53.33 = 105 m/s

Discussion

7765.	When will the relative velocity of two moving objects be zero?
Answer» When the two objects are moving with equal same speed and in the same direction.

Discussion

7766.	Shows the X- t plot of onedimensional motion of a particle. Is it correct to say from the graph that the particle moves in a straight line for t < 0 and on a parabolic path for t > 0? If not, suggest a suitable physical context for this graph.
Answer» No, it is wrong to make such statements about the trajectory of the particle because an x-t graph does not show the particle’s trajectory. Context: Consider a body dropped from the top of a tower at time t = 0. If the vertically downward direction is chosen as the positive direction, then the body’s x -t graph would resemble the one given in the question.

7766.

Shows the X- t plot of onedimensional motion of a particle. Is it correct to say from the graph that the particle moves in a straight line for t < 0 and on a parabolic path for t > 0? If not, suggest a suitable physical context for this graph.

Answer»

No, it is wrong to make such statements about the trajectory of the particle because an x-t graph does not show the particle’s trajectory.

Context:

Consider a body dropped from the top of a tower at time t = 0. If the vertically downward direction is chosen as the positive direction, then the body’s x -t graph would resemble the one given in the question.

Discussion

7767.	A LASER is a source of very intense, monochromatic, and unidirectional beam of light. These properties of laser light can be exploited to measure long distances. The distance of the Moon from the Earth has been already determined very precisely using a laser as a source of light. A laser light beamed at the Moon takes 2.56 s to return after reflection at the Moon’s surface. How much Is the radius of the lunar orbit around the Earth?
Answer» Time for the laser reach the moon = 1/2 × 2.56 s = 1.28 s ∴ Distance from the Earth to the moon = 1.28 s × speed of light in vacuum = 1.28 × 3 × 10⁸ms^-1 = 3.84 × 10⁸m ∴ The radius of the lunar orbit = 3.84 × 10⁸m.

7767.

A LASER is a source of very intense, monochromatic, and unidirectional beam of light. These properties of laser light can be exploited to measure long distances. The distance of the Moon from the Earth has been already determined very precisely using a laser as a source of light. A laser light beamed at the Moon takes 2.56 s to return after reflection at the Moon’s surface. How much Is the radius of the lunar orbit around the Earth?

Answer»

Time for the laser reach the moon

= 1/2 × 2.56 s = 1.28 s

∴ Distance from the Earth to the moon

= 1.28 s × speed of light in vacuum = 1.28 × 3 × 10⁸ms^-1

= 3.84 × 10⁸m

∴ The radius of the lunar orbit = 3.84 × 10⁸m.

Discussion

7768.	A laser is a source of very intense, mono-chromatic and unidirectional beam of light. These properties of a leaser light can be exploited to measure long distances. The distance of the MOON from the Earth has been already determined very precisely using a laser as source of light. A laser light beamed at Moon takes 2.56 seconds to return after reflection at the the moon's surface.How much is the radius of the lunar orbit around the Earth?
Answer» As v = 2d/t ⇒ d = v x t/2 = (3 x 10⁸ x 2.56/2) = 3.84 x 10⁸ m.

7768.

A laser is a source of very intense, mono-chromatic and unidirectional beam of light. These properties of a leaser light can be exploited to measure long distances. The distance of the MOON from the Earth has been already determined very precisely using a laser as source of light. A laser light beamed at Moon takes 2.56 seconds to return after reflection at the the moon's surface.How much is the radius of the lunar orbit around the Earth?

Answer»

As v = 2d/t

⇒ d = v x t/2 = (3 x 10⁸ x 2.56/2) = 3.84 x 10⁸ m.

Discussion

7769.	A LASER is a source of very intense, monochromatic, and unidirectional beam of light. These properties of a laser light can be exploited to measure long distances. The distance of the Moon from the Earth has been already determined very precisely using a laser as a source of light. A laser light beamed at the Moon takes 2.56 s to return after reflection at the Moon’s surface. How much is the radius of the lunar orbit around the Earth?
Answer» Time taken by the laser beam to return to Earth after reflection from the Moon = 2.56 s Speed of light = 3 × 10⁸ m/s Time taken by the laser beam to reach Moon = 1/2 x 2.56=1.28s Radius of the lunar orbit = Distance between the Earth and the Moon = 1.28 × 3 × 10⁸ = 3.84 × 10⁸ m = 3.84 × 10⁵km

Discussion

7770.	Figure 3.21 shows the x-t plot of one-dimensional motion of a particle. Is it correct to say from the graph that the particle moves in a straight line for t < 0 and on a parabolic path for t > 0? If not, suggest a suitable physical context for this graph.
Answer» No. The x-t graph of a particle moving in a straight line for t < 0 and on a parabolic path for t > 0 cannot be shown as the given graph. This is because, the given particle does not follow the trajectory of path followed by the particle as t = 0, x = 0. A physical situation that resembles the above graph is of a freely falling body held for sometime at a height

7770.

Figure 3.21 shows the x-t plot of one-dimensional motion of a particle. Is it correct to say from the graph that the particle moves in a straight line for t < 0 and on a parabolic path for t > 0? If not, suggest a suitable physical context for this graph.

Answer»

No.

The x-t graph of a particle moving in a straight line for t < 0 and on a parabolic path for t > 0 cannot be shown as the given graph. This is because, the given particle does not follow the trajectory of path followed by the particle as t = 0, x = 0. A physical situation that resembles the above graph is of a freely falling body held for sometime at a height

Discussion

7771.	The velocity-time graph of a particle in one-dimensional motion is shown in Fig. 3.29:Which of the following formulae are correct for describing the motion of the particle over the time-interval t2 to t1?
Answer» The correct formulae describing the motion of the particle are (c), (d) and, (f) The given graph has a non-uniform slope. Hence, the formulae given in (a), (b), and (e) cannot describe the motion of the particle. Only relations given in (c), (d), and (f) are correct equations of motion.

7771.

The velocity-time graph of a particle in one-dimensional motion is shown in Fig. 3.29:Which of the following formulae are correct for describing the motion of the particle over the time-interval t2 to t1?

Answer»

The correct formulae describing the motion of the particle are (c), (d) and, (f)

The given graph has a non-uniform slope.

Hence, the formulae given in (a), (b), and (e) cannot describe the motion of the particle.

Only relations given in (c), (d), and (f) are correct equations of motion.

Discussion

7772.	The velocity-time graph of a particle in one-dimensional motion is shown in Fig. 3.29:Which of the following formulae are correct for describing the motion of the particle over the time interval t2 to t1?(a) x(t2) = x(t1) + v(t1)(t2–t1) + (1/2)a(t2–t1)2(b) v(t2)= v(t1) + a(t2–t1)(c) vAverage = (x(t2) – x(t1)) / (t2 – t1)(d) aAverage = (v(t2) – v(t1)) / (t2 – t1)(e) x(t2) = x(t1) + vAverage(t2 – t1) +1/2)aAverage(t2 – t1)2(f) x(t2) – x(t1) = area under the v–t curve bounded by the t-axis and the dotted line shown.
Answer» The correct formulae describing the motion of the particle are (c), (d) and, (f) The given graph has a non-uniform slope. Hence, the formulae given in (a), (b), and (e) cannot describe the motion of the particle. Only relations given in (c), (d), and (f) are correct equations of motion.

Discussion

7773.	When do you say that a body is in motion?
Answer» A body is said to be in motion when it changes its position with respect to time and surrounding.

Discussion

7774.	A SONAR (sound navigation and ranging) uses ultrasonic waves to detect and locate objects under water. In a submarine equipped with a SONAR the time delay between generation of a probe wave and the reception of its echo after reflection from an enemy submarine is found to be 77.0 s. What is the distance of the enemy submarine? (Speed of sound in water = 1450 m s–1).
Answer» Let the distance between the ship and the enemy submarine be ‘S’. Speed of sound in water = 1450 m/s Time lag between transmission and reception of Sonar waves = 77 s In this time lag, sound waves travel a distance which is twice the distance between the ship and the submarine (2S). Time taken for the sound to reach the submarine = 1/2 x 77 = 38.5 s Therefore, Distance between the ship and the submarine (S) = 1450 × 38.5 = 55825 m = 55.8 km

Discussion

7775.	A sonar (sound navigation and ranging) used ultrasonic waves to detect and locate objects under water. In a submarine equipped with a SONAR the time delay between generation of a probe wave and the reception of its echo after reflection from an enemy submarine is found to be 77.0 s. What is the distance of the enemy submarine? (Speed of sound in water = 1450 ms-1)
Answer» AS d = v x 1/2 Given, v = 1450 ms^-1 and t = 77 s. we get d = 1450 x 77/2 = 55825 m = 55.8 km.

7775.

A sonar (sound navigation and ranging) used ultrasonic waves to detect and locate objects under water. In a submarine equipped with a SONAR the time delay between generation of a probe wave and the reception of its echo after reflection from an enemy submarine is found to be 77.0 s. What is the distance of the enemy submarine? (Speed of sound in water = 1450 ms-1)

Answer»

AS d = v x 1/2

Given, v = 1450 ms^-1 and t = 77 s.

we get d = 1450 x 77/2 = 55825 m = 55.8 km.

Discussion

7776.	A LASER is a source of very intense, monochromatic, and unidirectional beam of light. These properties of a laser light can be exploited to measure long distances. The distance of the Moon from the Earth has been already determined very precisely using a laser as a source of light. A laser light beamed at the Moon takes 2.56 s to return after reflection at the Moon’s surface. How much is the radius of the lunar orbit around the Earth?
Answer» Time taken by the laser beam to return to Earth after reflection from the Moon = 2.56 s Speed of light = 3 × 10⁸ m/s Time taken by the laser beam to reach Moon = (1/2) x 2.56 = 1.28s Radius of the lunar orbit = Distance between the Earth and the Moon = 1.28 × 3 × 10⁸ = 3.84 × 10⁸ m = 3.84 × 10⁵ km

7776.

A LASER is a source of very intense, monochromatic, and unidirectional beam of light. These properties of a laser light can be exploited to measure long distances. The distance of the Moon from the Earth has been already determined very precisely using a laser as a source of light. A laser light beamed at the Moon takes 2.56 s to return after reflection at the Moon’s surface. How much is the radius of the lunar orbit around the Earth?

Answer»

Time taken by the laser beam to return to Earth after reflection from the Moon = 2.56 s Speed of light = 3 × 10⁸ m/s

Time taken by the laser beam to reach Moon = (1/2) x 2.56 = 1.28s

Radius of the lunar orbit

= Distance between the Earth and the Moon

= 1.28 × 3 × 10⁸

= 3.84 × 10⁸ m = 3.84 × 10⁵ km

Discussion

7777.	Give example of a motion where x > 0, v < 0, a > 0 at a particular instant.
Answer» Example – x(t) = A + Be ^-γt Here, A > B and γ > 0 and all are positive constants.

7777.

Give example of a motion where x > 0, v < 0, a > 0 at a particular instant.

Answer»

Example – x(t) = A + Be ^-γt

Here, A > B and γ > 0 and all are positive constants.

Discussion

7778.	Give examples of a one-dimensional motion where(a) the particle moving along positive x-direction comes to rest periodically and moves forward.(b) the particle moving along positive x-direction comes to rest periodically and moves backward.
Answer» (i) x (t) = t - sin t (ii) x (t) = sin t

7778.

Give examples of a one-dimensional motion where(a) the particle moving along positive x-direction comes to rest periodically and moves forward.(b) the particle moving along positive x-direction comes to rest periodically and moves backward.

Answer»

(i) x (t) = t - sin t

(ii) x (t) = sin t

Discussion

7779.	Describe the selection of origin and sense of passage of time of a body performing one dimensional motion.
Answer» In one dimensional motion the initial instant of time or zero time (t = 0) is considered at the beginning of the observation of motion. It may not be the instant of beginning of motion. Suppose a ball is thrown from a height of 500 m. It becomes visible say at a height of 100 m. Then origin or initial instant of time or zero time (t = 0) is this instant only and not the instant when motion actually began. Thus, if zero instant is considered as present then times before the instant is past and time after this instant is future.

Discussion

7780.	The velocity-time graph of a particle in one-dimensional motion is shown in Fig.Which of the following formulae are correct for describing the motion of the particle over the time-interval t1 to t2
Answer» 1. Wrong, because it is not known whether the acceleration ‘a’ is constant. 2. Wrong, because it is not known whether the acceleration ‘a’ is constant. 3. Correct. By definition. 4. Correct. By definition 5. Wrong. The formula should contain v₁ (t) instead of v_average. 6. Correct By definition.

7780.

The velocity-time graph of a particle in one-dimensional motion is shown in Fig.Which of the following formulae are correct for describing the motion of the particle over the time-interval t1 to t2

Answer»

1. Wrong, because it is not known whether the acceleration ‘a’ is constant.

2. Wrong, because it is not known whether the acceleration ‘a’ is constant.

3. Correct. By definition.

4. Correct. By definition

5. Wrong. The formula should contain v₁ (t) instead of v_average.

6. Correct By definition.

Discussion

7781.	Read each statement below carefully and state with reasons and examples, if it is true or false; A particle in one-dimensional motion a) with zero speed at an instant may have non-zero acceleration at that instant b) with zero speed may have non-zero velocity, c) with constant speed must have zero acceleration, d) with positive value of acceleration must be speeding up.
Answer» a) True b) False c) True d) False Explanation: When an object is thrown vertically up in the air, its speed becomes zero at maximum height. However, it has acceleration equal to the acceleration due to gravity (g) that acts in the downward direction at that point. Speed is the magnitude of velocity. When speed is zero, the magnitude of velocity along with the velocity is zero. A car moving on a straight highway with constant speed will have constant velocity. Since acceleration is defined as the rate of change of velocity, acceleration of the car is also zero. This statement is false in the situation when acceleration is positive and velocity is negative at the instant time taken as origin. Then, for all the time before velocity becomes zero, there is slowing down of the particle. Such a case happens when a particle is projected upwards. This statement is true when both velocity and acceleration are positive, at the instant time taken as origin. Such a case happens when a particle is moving with positive acceleration or falling vertically downwards from a height.

7781.

Read each statement below carefully and state with reasons and examples, if it is true or false; A particle in one-dimensional motion a) with zero speed at an instant may have non-zero acceleration at that instant b) with zero speed may have non-zero velocity, c) with constant speed must have zero acceleration, d) with positive value of acceleration must be speeding up.

Answer»

a) True

b) False

c) True

d) False

Explanation:

When an object is thrown vertically up in the air, its speed becomes zero at maximum height. However, it has acceleration equal to the acceleration due to gravity (g) that acts in the downward direction at that point.

Speed is the magnitude of velocity. When speed is zero, the magnitude of velocity along with the velocity is zero.

A car moving on a straight highway with constant speed will have constant velocity. Since acceleration is defined as the rate of change of velocity, acceleration of the car is also zero.

This statement is false in the situation when acceleration is positive and velocity is negative at the instant time taken as origin. Then, for all the time before velocity becomes zero, there is slowing down of the particle. Such a case happens when a particle is projected upwards.

This statement is true when both velocity and acceleration are positive, at the instant time taken as origin. Such a case happens when a particle is moving with positive acceleration or falling vertically downwards from a height.

Discussion

7782.	A SONAR (sound navigation and ranging) uses ultrasonic waves to detect and locate objects under water. In a submarine equipped with a SONAR the time delay between generation of a probe wave and the reception of its echo after reflection from an enemy submarine is found to be 77.0 s. What is the distance of the enemy submarine? (Speed of sound in water = 1450 m s–1 ).
Answer» Let the distance between the ship and the enemy submarine be ‘S’. Speed of sound in water = 1450 m/s Time lag between transmission and reception of Sonar waves = 77 s In this time lag, sound waves travel a distance which is twice the distance between the ship and the submarine (2S). Time taken for the sound to reach the submarine = 1/2 x 77 = 38.5 s Distance between the ship and the submarine (S) = 1450 × 38.5 = 55825 m = 55.8 km

7782.

A SONAR (sound navigation and ranging) uses ultrasonic waves to detect and locate objects under water. In a submarine equipped with a SONAR the time delay between generation of a probe wave and the reception of its echo after reflection from an enemy submarine is found to be 77.0 s. What is the distance of the enemy submarine? (Speed of sound in water = 1450 m s–1 ).

Answer»

Let the distance between the ship and the enemy submarine be ‘S’.

Speed of sound in water = 1450 m/s

Time lag between transmission and reception of Sonar waves = 77 s

In this time lag, sound waves travel a distance which is twice the distance between the ship and the submarine (2S).

Time taken for the sound to reach the submarine = 1/2 x 77 = 38.5 s

Distance between the ship and the submarine (S) = 1450 × 38.5 = 55825 m = 55.8 km

Discussion

7783.

Differentiate between radiation and conduction.

Answer»

Radiation	Conduction
1. No medium is required.	1. Medium is required.
2. Heat radiation do not heat the intervening medium.	2.Energy is heated.
3. Heat radiations travel with speed of light.	3.It is slow mode of transmission of heat.

Discussion

7784.	Give examples of a one-dimensional motion where(a) the particle moving along positive x-direction comes to rest periodically and moves forward. .(b) the particle moving along positive x-direction comes to rest periodically and moves backward.
Answer» (a) Example – x(t) = t – sin t (b) Example – x(t) = sin t

7784.

Give examples of a one-dimensional motion where(a) the particle moving along positive x-direction comes to rest periodically and moves forward. .(b) the particle moving along positive x-direction comes to rest periodically and moves backward.

Answer»

(a) Example – x(t) = t – sin t

(b) Example – x(t) = sin t

Discussion

7785.	The farthest objects in our Universe discovered by modern astronomers are so distant that light emitted by them takes billions of years to reach the Earth. These objects (known as quasars) have many puzzling features, which have not yet been satisfactorily explained. what is the distance in km of a quasar from which light takes 3.0 billion years to reach us?
Answer» Given t = 3 x 10⁹ years = 3 x 10⁹ x 365.25 x 60 x 60 s c = 3 x 10⁵ km s^-1 (velocity of e.m. waves) d = c x t = 3 x 10⁵x 3 x 10⁹ x 365.25 x 24 x 60 x 60 = 2840184 x 10¹⁶ km = 2.84 x 10²² km.

7785.

The farthest objects in our Universe discovered by modern astronomers are so distant that light emitted by them takes billions of years to reach the Earth. These objects (known as quasars) have many puzzling features, which have not yet been satisfactorily explained. what is the distance in km of a quasar from which light takes 3.0 billion years to reach us?

Answer»

Given t = 3 x 10⁹ years

= 3 x 10⁹ x 365.25 x 60 x 60 s

c = 3 x 10⁵ km s^-1 (velocity of e.m. waves)

d = c x t = 3 x 10⁵x 3 x 10⁹ x 365.25 x 24 x 60 x 60

= 2840184 x 10¹⁶ km

= 2.84 x 10²² km.

Discussion

7786.	The farthest objects in our Universe discovered by modern astronomers are so distant that light emitted by them takes billions of years to reach the Earth. These objects (known as quasars) have many puzzling features, which have not yet been satisfactorily explained. What is the distance in km of a quasar from which light takes 3.0 billion years to reach us?
Answer» Time taken by quasar light to reach Earth = 3 billion years = 3 × 10⁹ years = 3 × 10⁹ × 365 × 24 × 60 × 60s Speed of light = 3 × 10⁸ m/s Distance between the Earth and quasar = (3 × 10⁸ ) × (3 × 10⁹ × 365 × 24 × 60 × 60) = 283824 × 10²⁰ m = 2.8 × 10²² km

7786.

The farthest objects in our Universe discovered by modern astronomers are so distant that light emitted by them takes billions of years to reach the Earth. These objects (known as quasars) have many puzzling features, which have not yet been satisfactorily explained. What is the distance in km of a quasar from which light takes 3.0 billion years to reach us?

Answer»

Time taken by quasar light to reach Earth = 3 billion years = 3 × 10⁹ years

= 3 × 10⁹ × 365 × 24 × 60 × 60s

Speed of light = 3 × 10⁸ m/s

Distance between the Earth and quasar

= (3 × 10⁸ ) × (3 × 10⁹ × 365 × 24 × 60 × 60)

= 283824 × 10²⁰ m = 2.8 × 10²² km

Discussion

7787.	Can earth be regarded as a point object if only orbital motion of earth around the sun is considered? Why?
Answer» Yes. This is because the size of earth is very small as compared to the size of the orbit of the earth around the sun.

Discussion

7788.	The farthest objects in our Universe discovered by modern astronomers are so distant that light emitted by them takes billions of years to reach the Earth. These objects (known as quasars) have many puzzling features, which have not yet been satisfactorily explained. What is the distance in km of a quasar from which light takes 3.0 billion years to reach us?
Answer» Distance of the quasar from the earth = Distance travelled by light in 3 billion years = 3 × 10⁵ kms^-1 × 3 × 10⁹ × 365 × 24 × 3600 = 2.8 × 10²² km.

7788.

The farthest objects in our Universe discovered by modern astronomers are so distant that light emitted by them takes billions of years to reach the Earth. These objects (known as quasars) have many puzzling features, which have not yet been satisfactorily explained. What is the distance in km of a quasar from which light takes 3.0 billion years to reach us?

Answer»

Distance of the quasar from the earth = Distance travelled by light in 3 billion years

= 3 × 10⁵ kms^-1 × 3 × 10⁹ × 365 × 24 × 3600

= 2.8 × 10²² km.

Discussion

7789.	What is a unit?
Answer» The standard quantity in terms of which a physical quantity is measured is called the unit of that physical quantity.

Discussion

7790.	In which of the following examples of motion, can the body be considered approximately a point object:a) A railway carriage moving without jerks between two stations. b) A monkey sitting on top of a man cycling smoothly on a circular track. c) A spinning cricket ball that turns sharply on hitting the ground. d) A tumbling beaker that has slipped off the edge of a table
Answer» (a), (b) The size of a carriage is very small as compared to the distance between two stations. Therefore, the carriage can be treated as a point sized object. The size of a monkey is very small as compared to the size of a circular track. Therefore, the monkey can be considered as a point sized object on the track. The size of a spinning cricket ball is comparable to the distance through which it turns sharply on hitting the ground. Hence, the cricket ball cannot be considered as a point object. The size of a beaker is comparable to the height of the table from which it slipped. Hence, the beaker cannot be considered as a point object.

7790.

In which of the following examples of motion, can the body be considered approximately a point object:a) A railway carriage moving without jerks between two stations. b) A monkey sitting on top of a man cycling smoothly on a circular track. c) A spinning cricket ball that turns sharply on hitting the ground. d) A tumbling beaker that has slipped off the edge of a table

Answer»

(a), (b)

The size of a carriage is very small as compared to the distance between two stations. Therefore, the carriage can be treated as a point sized object.

The size of a monkey is very small as compared to the size of a circular track. Therefore, the monkey can be considered as a point sized object on the track.

The size of a spinning cricket ball is comparable to the distance through which it turns sharply on hitting the ground. Hence, the cricket ball cannot be considered as a point object.

The size of a beaker is comparable to the height of the table from which it slipped. Hence, the beaker cannot be considered as a point object.

Discussion

7791.	Find the kinetic energy of four moles of a diatomic gas at 400 K.
Answer» Data : n = 4, T = 400 K, R = 8.314 J/mol. K The kinetic energy of four moles of the gas = \(\frac52\) nRT = \((\frac52)\) (8.314) (400) J = (40)(8.314 × 10²) J = 3.326 × 10⁴ J

7791.

Find the kinetic energy of four moles of a diatomic gas at 400 K.

Answer»

Data : n = 4, T = 400 K, R = 8.314 J/mol. K

The kinetic energy of four moles of the gas

= \(\frac52\) nRT = \((\frac52)\) (8.314) (400) J

= (40)(8.314 × 10²) J

= 3.326 × 10⁴ J

Discussion

7792.	What is the kinetic energy per unit volume of a gas if the gas pressure is 105 N/m2 ?
Answer» Kinetic energy per unit volume of a gas = \(\frac32\)P = \(\frac32\) x 10⁵ = 1.5 x 10⁵ j/m³.

7792.

What is the kinetic energy per unit volume of a gas if the gas pressure is 105 N/m2 ?

Answer»

Kinetic energy per unit volume of a gas

= \(\frac32\)P = \(\frac32\) x 10⁵ = 1.5 x 10⁵ j/m³.

Discussion

7793.	Two waves of equal amplitude A, and equal frequency travel in the same direction in a medium. The amplitude of the resultant wave is.(a) 0(b) A(c) 2A(d) between 0 and 2A.
Answer» (d) between 0 and 2A. EXPLANATION: The amplitude of the resultant wave depends on the phase difference between the two waves. If the phase difference is zero then the resultant amplitude is maximum = A+A = 2A. But if the phase difference is π, then the resultant amplitude is minimum =A-A = 0. So the amplitude of the resultant wave is between 0 and 2A depending on the phase difference.

7793.

Two waves of equal amplitude A, and equal frequency travel in the same direction in a medium. The amplitude of the resultant wave is.(a) 0(b) A(c) 2A(d) between 0 and 2A.

Answer»

(d) between 0 and 2A.

EXPLANATION:

The amplitude of the resultant wave depends on the phase difference between the two waves. If the phase difference is zero then the resultant amplitude is maximum = A+A = 2A. But if the phase difference is π, then the resultant amplitude is minimum =A-A = 0. So the amplitude of the resultant wave is between 0 and 2A depending on the phase difference.

Discussion

7794.	Two waves represented by y = a sin(ωt - kx) and y = a cos(ωt - kx) are superposed. The resultant wave will have an amplitude(a) a(b)√2a(c) 2a(d) 0.
Answer» The correct answer is (b)√2a EXPLANATION: When two waves are superimposed, the displacements of the particle due to each wave is added. Hence the resultant wave is given as y' = a sin(⍵t-kx) + a cos(⍵t-kx) →y' = a {sin(⍵t-kx) + sin(π/2+⍵t-kx)} →y'=a2 sin{(⍵t-kx+π/2+⍵t-kx)/2}cos{(⍵t-kx-π/2-⍵t+kx)/2} →y' = 2a sin(⍵t-kx+π/4)*cosπ/4 →y' = (2a/√2) sin(⍵t-kx+π/4) →y' =√2a sin(⍵t-kx+π/4) Clearly the amplitude of the resultant wave is √2a.

7794.

Two waves represented by y = a sin(ωt - kx) and y = a cos(ωt - kx) are superposed. The resultant wave will have an amplitude(a) a(b)√2a(c) 2a(d) 0.

Answer»

The correct answer is (b)√2a

EXPLANATION:

When two waves are superimposed, the displacements of the particle due to each wave is added. Hence the resultant wave is given as

y' = a sin(⍵t-kx) + a cos(⍵t-kx)

→y' = a {sin(⍵t-kx) + sin(π/2+⍵t-kx)}

→y'=a*2 sin{(⍵t-kx+π/2+⍵t-kx)/2}*cos{(⍵t-kx-π/2-⍵t+kx)/2}

→y' = 2a sin(⍵t-kx+π/4)*cosπ/4

→y' = (2a/√2) sin(⍵t-kx+π/4)

→y' =√2a sin(⍵t-kx+π/4)

Clearly the amplitude of the resultant wave is √2a.

Discussion

7795.	The equation y = A sin2(kx -ωt) represents a wave motion with(a) amplitude A, frequency ω/2π (b) amplitude A/2, frequency ω/π(c) amplitude 2A, frequency ω/4π(d) does not represent a wave motion.
Answer» (b) amplitude A/2, frequency ω/π EXPLANATION: y = A sin²(kx-⍵t) →y =½A{1-cos(2kx-2⍵t)} →y' = ½Acos(2kx-2⍵t) It represents a wave motion with amplitude A/2 and frequency 2⍵/2π i.e. ⍵/π

7795.

The equation y = A sin2(kx -ωt) represents a wave motion with(a) amplitude A, frequency ω/2π (b) amplitude A/2, frequency ω/π(c) amplitude 2A, frequency ω/4π(d) does not represent a wave motion.

Answer»

(b) amplitude A/2, frequency ω/π

EXPLANATION:

y = A sin²(kx-⍵t)

→y =½A*{1-cos(2kx-2⍵t)}

→y' = ½A*cos(2kx-2⍵t)

It represents a wave motion with amplitude A/2 and frequency 2⍵/2π i.e. ⍵/π

Discussion

7796.	A sine wave is travelling in a medium. A particular particle has zero displacements at a certain instant. The particle closest to it having zero displacements is at a distance(a) λ/4 (b) λ/3(c) λ/2(d) λ.
Answer» The correct answer is (c) λ/2 EXPLANATION: The particles at distance λ/2 have always the same displacement. So the closest zero displacement particle will be at λ/2 distance away.

7796.

A sine wave is travelling in a medium. A particular particle has zero displacements at a certain instant. The particle closest to it having zero displacements is at a distance(a) λ/4 (b) λ/3(c) λ/2(d) λ.

Answer»

The correct answer is (c) λ/2

EXPLANATION:

The particles at distance λ/2 have always the same displacement. So the closest zero displacement particle will be at λ/2 distance away.

Discussion

7797.	A cork floating in a calm pond executes simple harmonic motion of frequency v when a wave generated by a boat passes by it. The frequency of the wave is(a) v(b) v/2(c) 2v(d) √2V.
Answer» The correct answer is (a) v EXPLANATION: The time taken by the wave in moving one wavelength is exactly the same as in moving the cork one oscillation. Hence the frequency of the wave is equal to the frequency of the cork.

7797.

A cork floating in a calm pond executes simple harmonic motion of frequency v when a wave generated by a boat passes by it. The frequency of the wave is(a) v(b) v/2(c) 2v(d) √2V.

Answer»

The correct answer is (a) v

EXPLANATION:

The time taken by the wave in moving one wavelength is exactly the same as in moving the cork one oscillation. Hence the frequency of the wave is equal to the frequency of the cork.

Discussion

7798.	Two particles A and B have a phase difference of n when a sine wave passes through the region.(a) A oscillates at half the frequency of B.(b) A and B move in opposite directions.(c) A and B must be separated by half of the wavelength.(d) The displacements at A and B have equal magnitudes.
Answer» (b) A and B move in opposite directions. (d) The displacements at A and B have equal magnitudes. EXPLANATION: The frequencies of the particles will be the same, so the option (a) is not true. Let the displacement of the particle at A be y = A' sin(⍵t-kx) and of the particle at B be y' = A' sin(⍵t-kx+π) = -A' sin(⍵t-kx) So, y = -y'. Thus A and B move in opposite directions and the displacements at A and B have equal magnitudes. So, the options (b) and (d) are true. When the phase difference of A and B is π, the separation between them maybe (nλ+λ/2) = (2n+1)λ/2, where n = 1, 2, 3,....... The option (c) is a special case, hence not true.

7798.

Two particles A and B have a phase difference of n when a sine wave passes through the region.(a) A oscillates at half the frequency of B.(b) A and B move in opposite directions.(c) A and B must be separated by half of the wavelength.(d) The displacements at A and B have equal magnitudes.

Answer»

(b) A and B move in opposite directions.

(d) The displacements at A and B have equal magnitudes.

EXPLANATION:

The frequencies of the particles will be the same, so the option (a) is not true.

Let the displacement of the particle at A be y = A' sin(⍵t-kx) and of the particle at B be y' = A' sin(⍵t-kx+π) = -A' sin(⍵t-kx)

So, y = -y'.

Thus A and B move in opposite directions and the displacements at A and B have equal magnitudes.

So, the options (b) and (d) are true.

When the phase difference of A and B is π, the separation between them maybe (nλ+λ/2) = (2n+1)λ/2, where n = 1, 2, 3,....... The option (c) is a special case, hence not true.

Discussion

7799.	A tuning fork sends sound waves in air. If the temperature of the air increases, which of the following parameters will change ?(a) Displacement amplitude.(b) Frequency.(c) Wavelength .(d) Time period .
Answer» (c) Wavelength . EXPLANATION: When the sound wave is being sent by a tuning fork, its displacement amplitude, frequency and the time period will remain the same even if the temperature changes. Since the velocity of the sound V ∝ √T where T is the temperature in °K. Thus with the increase in temperature V increases, but = V/ν. Here ν is constant hence with the increase in V the wavelength also increases. Hence the option (c).

7799.

A tuning fork sends sound waves in air. If the temperature of the air increases, which of the following parameters will change ?(a) Displacement amplitude.(b) Frequency.(c) Wavelength .(d) Time period .

Answer»

(c) Wavelength .

EXPLANATION:

When the sound wave is being sent by a tuning fork, its displacement amplitude, frequency and the time period will remain the same even if the temperature changes. Since the velocity of the sound V ∝ √T where T is the temperature in °K. Thus with the increase in temperature V increases, but = V/ν. Here ν is constant hence with the increase in V the wavelength also increases. Hence the option (c).

Discussion

7800.

In a stationary wave,(a) all the particles of the medium vibrate in phase(b) all the antinodes vibrate in phase(c) the alternate antinodes vibrate in phase(d) all the particles between consecutive nodes vibrate in phase.

Answer»

(c) the alternate antinodes vibrate in phase

(d) all the particles between consecutive nodes vibrate in phase.

EXPLANATION:

In a stationary wave, all the particles between consecutive nodes vibrate in phase. Option (d) is correct. The particles on the different sides of a node do not vibrate in phase but they have a phase difference of π. So the alternate parts between the consecutive nodes vibrate in phase. Thus the options (a) and (b) are not true but (c) is true.

Discussion

Explore topic-wise InterviewSolutions in .

When two bodies move uniformly towards each other, the distance between them diminishes by 16 m every 10s. If the bodies move with vlocitics of the same magnitude and in the same direction as before, the distance between them will increase by 3m every 5s. What is velocity of each body?

Is the time variation of position shown in the Fig. alongside, observed in nature?

Figure shows a displacements time graph. Comment on the sign of velocities at point P, Q, R, S and T.

Velocity-time plot of two particles make angles of 60º and 30º with the axis on which time is plotted. What is the ratio of their acceleration?

When is the relative velocity of two bodies maximum?

The (x -t) graph of a moving particle is shown in the figure below. Comment on the signs of the velocities at the points C,D,E and F.

Two balls have same size but one is dense. When released simultaneously from same height which ball will reach the ground first?

Two balls of different masses are thrown vertically upward with same initial speed. Which one will rise to a greater height?

Write the characteristics of displacement?

Look at the graphs (a) to (d) (Fig.) carefully and state, with reasons, which of these cannot possibly represent onedimensional motion of a particle.

An automobile moving with a uniform velocity of 500 ms-1 is brought to rest in travelling a distance of 5m. What is the acceleration produced by the brakes?

Look at the graphs (a) to (d) (Fig. 3.20) carefully and state, with reasons, which of these cannot possibly represent one-dimensional motion of a particle.

When will the relative velocity of two moving objects be zero?

Shows the X- t plot of onedimensional motion of a particle. Is it correct to say from the graph that the particle moves in a straight line for t &lt; 0 and on a parabolic path for t &gt; 0? If not, suggest a suitable physical context for this graph.

Figure 3.21 shows the x-t plot of one-dimensional motion of a particle. Is it correct to say from the graph that the particle moves in a straight line for t &lt; 0 and on a parabolic path for t &gt; 0? If not, suggest a suitable physical context for this graph.

The velocity-time graph of a particle in one-dimensional motion is shown in Fig. 3.29:Which of the following formulae are correct for describing the motion of the particle over the time-interval t2 to t1?

When do you say that a body is in motion?

Give example of a motion where x &gt; 0, v &lt; 0, a &gt; 0 at a particular instant.

Give examples of a one-dimensional motion where(a) the particle moving along positive x-direction comes to rest periodically and moves forward.(b) the particle moving along positive x-direction comes to rest periodically and moves backward.

Describe the selection of origin and sense of passage of time of a body performing one dimensional motion.

The velocity-time graph of a particle in one-dimensional motion is shown in Fig.Which of the following formulae are correct for describing the motion of the particle over the time-interval t1 to t2

Differentiate between radiation and conduction.

Give examples of a one-dimensional motion where(a) the particle moving along positive x-direction comes to rest periodically and moves forward. .(b) the particle moving along positive x-direction comes to rest periodically and moves backward.

Can earth be regarded as a point object if only orbital motion of earth around the sun is considered? Why?

What is a unit?

Find the kinetic energy of four moles of a diatomic gas at 400 K.

What is the kinetic energy per unit volume of a gas if the gas pressure is 105 N/m2 ?

Two waves of equal amplitude A, and equal frequency travel in the same direction in a medium. The amplitude of the resultant wave is.(a) 0(b) A(c) 2A(d) between 0 and 2A.

Two waves represented by y = a sin(ωt - kx) and y = a cos(ωt - kx) are superposed. The resultant wave will have an amplitude(a) a(b)√2a(c) 2a(d) 0.

The equation y = A sin2(kx -ωt) represents a wave motion with(a) amplitude A, frequency ω/2π (b) amplitude A/2, frequency ω/π(c) amplitude 2A, frequency ω/4π(d) does not represent a wave motion.

A sine wave is travelling in a medium. A particular particle has zero displacements at a certain instant. The particle closest to it having zero displacements is at a distance(a) λ/4 (b) λ/3(c) λ/2(d) λ.

A cork floating in a calm pond executes simple harmonic motion of frequency v when a wave generated by a boat passes by it. The frequency of the wave is(a) v(b) v/2(c) 2v(d) √2V.

Two particles A and B have a phase difference of n when a sine wave passes through the region.(a) A oscillates at half the frequency of B.(b) A and B move in opposite directions.(c) A and B must be separated by half of the wavelength.(d) The displacements at A and B have equal magnitudes.

A tuning fork sends sound waves in air. If the temperature of the air increases, which of the following parameters will change ?(a) Displacement amplitude.(b) Frequency.(c) Wavelength .(d) Time period .

In a stationary wave,(a) all the particles of the medium vibrate in phase(b) all the antinodes vibrate in phase(c) the alternate antinodes vibrate in phase(d) all the particles between consecutive nodes vibrate in phase.

Shows the X- t plot of onedimensional motion of a particle. Is it correct to say from the graph that the particle moves in a straight line for t < 0 and on a parabolic path for t > 0? If not, suggest a suitable physical context for this graph.

Figure 3.21 shows the x-t plot of one-dimensional motion of a particle. Is it correct to say from the graph that the particle moves in a straight line for t < 0 and on a parabolic path for t > 0? If not, suggest a suitable physical context for this graph.

Give example of a motion where x > 0, v < 0, a > 0 at a particular instant.