1971 + Interview Questions in Physics in Class 9 Page 14 InterviewSolution

651.	A farmer moves along the boundry of a square field of side 10M in 40s. What will be the magnitude of displacement of the farmer at the end of 2 minutes 20 seconds from his initial position?
Answer» Solution :The distance covered in one round of the field = the perimeter of the field `= 4 xx 10 m = 40 m` Time taken by the farmer to complette one round. i.e., 40 m is 40 second. ln 2 minute 20 second i.e., 140 second the farmer covers a distance of 140m. One round = 40 m ` therefore m = (140)/(40) =3.4` rounds `0.5` rounds ` 0.5 xx 40 m = 20 m` If the farmeer starts from POINT A, then at the end of 2 min 20 s he will be at the point C. `therefore` The displacement is AC. To find the magnitude of AC, use pythagoras. theorem. In right ANGLED triangle ABC, `AC ^(2) = AB^(2) + BC ^(2)` =`(10)^(2) + (10) ^(2)` `= 100 + 100 = 200` `therefore AC SQRT (200) = sqrt (100 xx2 ) = 10 sqrt2 m ` The magnitude of displacement of the farmer is `10 sqrt2 m.` The distance travelled by the farmer is 140 m.

Discussion

652.	What is radioactivity? What is the cause for natural radioactivity ?
Answer»

Discussion

653.	Relative density of a substance is expressed by comparing the density of that substance with the density of:
Answer» air mercury water iron Answer :C

Discussion

654.	Four beakers are labelled as P,Q,R and S. A student puts salt solutions of different concentrations in the four beakers without spring balance gives a reading of 150g in air. When this solid, while still suspended from the hook of spring balance, is fully immersed in beakers P,Q,R and S, the readings shown by the spring balance in the four beakers P,Q,R and S are 110g,130g, 140g and 120g respectively. The most concentrated solution is contained in the beaker labelled as:
Answer» P Q R S Answer :A

Discussion

655.	A body of weight 10 N sinks in water. Weight of the water displaced is 2N. Which principle is related to this?
Answer» ANSWER :ARCHIMEDES PRINCIPLE

Discussion

656.	Arvind is a student of class IX. One day he had to visit a dentist in the morning because of severe toothache, so he reached late in the school. At that time, his classmates were doing physics experiments in the science laboratory. The science teacher, Mr. Bhatia, asked Arvind to stand alongside Rahul and observe carefully what he was doing. Rahul took a glass tumbler and placed a thick square card on its mouth. He then placed a coin above this card in middle. Rahul flicked the card hard with his fingers. On flicking, the card moved away but the coin dropped into the glass tumbler. After the experiment was over, Mr. Bhatia, asked Arvind to answer the following questions: (a) What is the 'initial state' of the card? Why does the card move away when flicked with fingers? (b) What is the 'initial state' of the coin? Why does coin not move away when the card is flicked with fingers? (c) Which property of coin is exhibited by the fact that the coin drops into glass tumbler when card is flicked away with fingers and moves away? Explain your answer. (d) What was Rahul trying to illustrate by performing this experiment? (e) What values are displayed by Arvind in this episode?
Answer» SOLUTION :(a) The 'initial state' of the card is that of 'rest' (or 'stationary'). When the card is flicked (or hit) with fingers, then a FORCE acts on the card and changes its state of 'rest' to that of 'motion'. Due to this, the card moves AWAY from the mouth of glass tumbler. (b) The 'initial state' of the coin is also that of 'rest' (or 'stationary'). when the card is flicked (or hit) with fingers, then the force exerted by fingers does not act on the coin placed on the card and hence the coin does not move away (the force of flick acts only on the card) (c) Since the force of flick of fingers does not act on the coin placed on the card, the coin CONTINUES to be in its 'state of rest' due to 'inertia' and drops into the glass tumbler (when the card below moves away). So, the coin exhibits the property of 'inertia'. (d) Rahul was trying to illustrate Newton'sfirst law of motion by performing this EXPERIMENT. (e) The valyes displayed by Arvind in this episode are (i) Keen observation (ii) Knowledge of Newton's first law of motion, and (iii) Ability to apply knowledge in solving problems.

Discussion

657.	What is lactometer and hydrometer ?
Answer» Solution :LACTOMETER is a DEVICE used to FIND the purity of a GIVEN sample of milk. Hydrometer is a device used to find the DENSITY of liquids

Discussion

658.	What happens to speed, velocity, acceleration when an object moves in a circle with uniform speed?
Answer» Solution :Speed remains CONSTANT, VELOCITY, MAGNITUDE REMAIN constant, but direction changes continuouly. Acceleration and magnitude remains constant but direction changes CONTINUOUSLY.

Discussion

659.	A spring balance shows 100 gf reading when a metallic sphere is suspended from its hook. When the completely immersed in water, the reading shown by the balance is 75gf. The relative density of the material of the sphere is
Answer» 1 2 3 4 Answer :D

Discussion

660.	Select conductors of electricity from the following : Copper wire, silk thread, pure water, acidulated water,human body, glass, mercury.
Answer» Answer :Copper WIRE, acidulated WATER, HUMAN BODY and mercury.

Discussion

661.	Examine the graph and answer the following question. Say whether the acceleration from O to A is uniform? What about from A to B?
Answer» Answer :`O -> A` uniform ACCELERATION (`0.4m / s^2`) `A-> B` uniform RETARDATION(`1M / s^2)

Discussion

662.	A piece of brass weighs 175 gf in air and 150 gf when fully immersed in water. The density of water is 1.0gcm^(-3).(i) What is the volume of the brass piece ? (ii) Why does the brass piece weigh less in water?
Answer» ANSWER :(i) `25CM^(3)` (II) due to UPTHRUST.

Discussion

663.	A pendulum clock becomes
Answer» ANSWER :GAIN

Discussion

664.	The unit of magnetical flux density is …………………….
Answer» WEBER weber/metre `"weber/meter"^(2)` `"weber.meter"^(2)` ANSWER :C

Discussion

665.	Where does a body experience maximum weight on the earth? What is the reason?
Answer» ANSWER :MAXIMUM weight experiences at the POLES. Because value of G is greater at the poles.

Discussion

666.	What does the odometer of an automobile measure?
Answer» SOLUTION :The odometer of an automobile measures the distance TRAVELLED by the automobile (or vehicle).

Discussion

667.	The kinetic energy of an object of mass, m moving with a velocity of 5m//s is 25J. What will be its kinetic energy when its velocity is double? What will be its Kinetic energy when its velocity is increased three times. When its velocity is increased three times.
Answer» Solution :K.E. of the object = 25 J Velocity of the object = 5 m/s K.E = `1/2 mv^(2)` m = `2 xx (K.E) / v^(2)` m = `2 xx (25)/(25) =` 2 KG If the velocity is double, `v=2xx5 =` 10m/s Therefor K.E (for v = 10 m/s) = `1/2 m^(2)` `= 1/2 xx 2x 100 = 100 J` If the velocity is tripled, `v = 3 xx 5` = 15 m/s Therefor K.E ( for v = 10 m/s) = `1/2 mv^(2)` = `1/2 xx 2x 225 = 225 J`

Discussion

668.	How long will sound take to travel in (a) an iron rail and (b) air, both 3.3 km in length ? Take speed of sound in air to be 330 m s^(-1) and in iron to be 5280 m s^(-1).
Answer» SOLUTION :(a) 0.625 s , (B) 10 s

Discussion

669.	The data regarding the motion of two different objects A and B are given in the following table : Examine them carefully and state whether the motion of the objects is uniform or non-uniform.
Answer» SOLUTION :The distance covered by OBJECT A is equal in equal intervals of time... object A SHOWS UNIFORM motion. The distance covered by object B is unequal in equal intervals of time.`therefore` object B shows non-uniform motion.

Discussion

670.	An object of weight 500 N sinks in water. Weight of water overflowed is 50 N. What is the weight of the object in water?
Answer» ANSWER :weight in WATER =Weight in air-weight of water over FLOWED`=500 N-50 N`=450 N`

Discussion

671.	Usha swims in a 90 m long pool. She covers 180 m in one minute by swimming from one end to the other and back along the same straight path. Find the average speed and average velocity of Usha.
Answer» Solution :TOTAL DISTANCE covered by Usha in 1 min is 180 m. Displacement of Usha in `1 min =0 m ` AVERAGE speed `= (" Total distance covered")/("Total time taken") = (180m )/(1 mn)` `= (180 m)/(1 min ) x (1 min)/(60 s)` `= 3 ms ^(-1)` Average velocity `= ("Displacement")/("Total time taken") = (0M)/(60S ) = 0 m s ^(-1)` The average speed of Usha is `3 ms ^(-1) and ` her average velocity is `0 ms ^(-1).`

Discussion

672.	Akhtar, kiran an rahul were riding in a motorcar that was moving with ahigh velocity on an expressway when an insect hit the windshied and got stuck on the windscreen. Akthar and kiran started pondering over the situation.. Kiran suggested that the inserctsuffered a greater change in momentum as compared to the change in momentum of the motorcar (because the change in the velocity of the insect was much more than that of the motorcar). Akthar said that since the motor car was moving with a larger velocity, it exerted a larger force on the insect. And as a result the insect died. Rahul while putting an entirely new explanation said that both the motorcar and the insect experieneced the same force and a change in their momentum comment on these suggestions.
Answer» Solution :The suggestion made by akthar that the motor CAR exerted a LARGER force on the insect because of large velocity of moter car is ALSO wrong. The explanation put forward by rahul is correct on collision of insect with moter car, both EXPERIENCE the same force as action and reaction are always equal and opposite. Further, changes in their momentums are also the same only signs of changes in momentum opposite, i.e, change in moments of the TWO occur in opposite directions, though magnitude of change in momntum of each is the same.

Discussion

673.	At what temperature the density of water is maximum? State its value.
Answer» ANSWER :At `4^(@)C, 1000 KGM^(-3)`

Discussion

674.	Name the type of waves produced when a tuning fork is struck in air.
Answer» ANSWER :LONGITUDINAL (SOUND) WAVES

Discussion

675.	When a point source of light is kept near a plane mirror
Answer» only thereflected rays closeto the normal meet at a point when produced BACKWARDS. only those raysreflected at SMALL angles meet when produced backwards. light of different colours form IMAGES of different sizes. all thereflected rays meet at a point when produced backwards. Solution :When a point SOURCE is KEPT near a plane mirror, all thereflected rays appear to meet at a point when produced backwards.

Discussion

676.	What is responsible for the flow of current through (i) a metallic conductor, (ii) an electrolyte?
Answer» Solution :(i) In a METALLIC conductor, FREE electrons are RESPONSIBLE for the flow of current. (ii) In an electrolyte, both the positive and NEGATIVE ions are responsible for the flow of current.

Discussion

677.	Three students A,B and C determined the volume of a solid by immersing it in water in the overflow cans set up The result obtained will be wrong for : (A) , (B) , (C) .
Answer» student A student B student C all THREE students. Solution :(d) The OVERFLOW can must be FILLED upto its spout.

Discussion

678.	How much heat energy is required to change 2 kg of ice at 0^@C into water at 20^@C? (Specific latent heat of fusion of water = 3,34,000J/kg, Specific heat capacity of water =4200 JKg^(-1) K^(-1) )
Answer» Solution :TOTAL heat =Heat required to convent 2kg of ice into water at `0^@` C + Heat required to CONVERT 2kg of water at `0^@C` to 2kg of water at `20^@C` Heat =m(hfw)+mc `DeltaT` Here, m (mass of ice )=2 KG hfw(specific LATENT heat of water ) =3,34,000 J/Kg C(specific heat capacity of water) =`4200 JKg^(-1)K^(-1)` `DeltaT` (Temperature difference ) =`20^@C` Therefore , Heat required = (2 x 334000 ) + (2 x 4200 ) (20-0) =668000+8400(20) =668000+168000 heat required =8,36,000 J

Discussion

679.	If this body is allowed to fall freely, will there be anychange in the force experienced by the body?
Answer» ANSWER :WEIGHT LESSENS OCCURS

Discussion

680.	Speed is a ____ quantity whereas velocity is a _____ quantity.
Answer» SOLUTION : SCALAR, VECTOR

Discussion

681.	Complete the following sentence : A longitudinal wave is composed of compression and ……………………. .
Answer» SOLUTION :RAREFACTION

Discussion

682.	The orbital velocity of a satellite is given by the expression V = sqrt((GM)/(R + h)), here M is the mass of the Earth, R is the radius of the Earth and 'h' is the height of the satellite from the surface of the Earth. Explain the reasons why the geostationary satellite is not possible to set in orbit around the Earth at two different heights from the surface of the Earth.
Answer» Solution :Can there be two GEOSTATIONARY orbits? - No - The time period of geostationary satellite is 24 hrs (or) 86400 seconds. We know, `T = 2 pi sqrt((1)/(g))` where 1 = (R + h) (or) (Radius of the EARTH + height of geostationary ORBIT from the SURFACE of the Earth) g = acceleration due to gravity at the geostationary orbit. But, `g = (GM)/((R + h)^(2))` `T = 2pi sqrt(((R + h)/(GM))/((R + h)^(2)))=2pi sqrt((R + h)^(3)/(GM))` Here, G, M, R are constants `rArr T alpha (R + h)^(3//2)` So, for only one value of 'h', 'T' will be equal to 24 hours. We can have only one geostationary orbit.

Discussion

683.	Define amplitude, time period and frequency of sound wave.
Answer» Solution :Amplitude : The magnitude of the maximum disturbance in the MEDIUM on either side of the mean value is called amplitude of the wave. Its UNIT is meter. TIME period: The time taken by two consecutive compression or rarefraction to cross a fixed point is called the time period of the wave. Frequency : The number of oscillation, occurring per unit time is called the frequency of sound wave.

Discussion

684.	When a piece of wood is suspended from the hook of a spring balance, it reads 70 gf. The wood is now lowered into water.What reading do you expect on the scale of spring balance?
Answer» ANSWER :ZERO

Discussion

685.	Define 1 J of work.
Answer» SOLUTION :1 J of work is said to be done when a force of 1 N ACTING on an OBJECT DISPLACES it in the direction of force through 1 metre.

Discussion

686.	An object is thrown vertically upwards with velocity of 20ms^(-1). At what height will its kinetic energy and potential energy be equal? (g=10ms^(-2))
Answer» `10m` `20m` `15m` `5m` Solution :`u=20ms^(-1)` As per the law of CONSERVATION of MECHANICAL energy, `(("Mechanical"),("energy of the"),("OBJECT on ground"))=(("Mechanical energy"),("of the object at"),("maximum height"))` `therefore E_(k_(1))+E_(p_(1))=E_(k_(2))+E_(p_(2))` `therefore (1)/(2)m u^(2)+0=0+mgh` (`because` Potential energy of the object on ground `E_(p_(1))=0` and kinetic energy of the object at the maximum height `E_(k_(2))=0`) `therefore h=(u^(2))/(2g)=((20)^(2))/(2xx10)=20m`

Discussion

687.	A unit positive charge is moved along the circumfer-ence of a circle of radius, r with a -5muC charge at the centre at the centre of the circle. Then, the work done in the process is "______".
Answer» negative work of `100 J` positive work of `100 J` zero `(Q.1)/(4pi in_(0).R)` ANSWER :C

Discussion

688.	Assertion (A) : Maximum sunlight reaches earth's surface during the afternoon time. Reason (R) : Heat from the sun reaches earth's surface by radiation.
Answer» If both assertion and REASON are true and reason is the correct explanation of assertion. If both assertion and reason are true butreason is not the correct explanation of assertion. If assertion is true but reason is false If assertion is false but reason is true ANSWER :B

Discussion

689.	Pulley is the most commonly used simple machine to draw water from a well since (A) its mechanical advantage is greater than one (B) it changes the direction of application of effort and makes it convenient to draw water
Answer» Only A is true Only B is true Both A ANDB are true Answer :B

Discussion

690.	What is the connection between electricity and magnetism?
Answer» Solution :Electricity and MAGNETISM are closely RELATED to each other. The CURRENT FLOWING through the wire produces a circular magnetic field outside the wire. The direction of this magnetic field depends on the electric current. Similarly, a changing magnetic field produces an electric current in a wire or conductor. The relationship between electricity and magnetism is called electromagnetism.

Discussion

691.	Name the radiations which are absorbed by the green house gases in the earth's atmosphere.
Answer» ANSWER :INFRARED RADIATION of LONG WAVELENGTH

Discussion

692.	Decribe the energy transformations that occur as the Earth orbits the sun in its ellipitcal orbit.
Answer» SOLUTION :CHANGES in gravitational POTENTIAL ENERGY are compenstated by changes in its kinetic energy so that its mechanicacl energy is conserved.

Discussion

693.	Constant speed oof a train is 54 kim h ^(-1). What is its speed in unit 'ms ^(-1).?
Answer» `15 ms ^(-1)` `90 ms ^(-1)` `1.5 ms ^(-1)` `9 ms ^(-1)` Solution :SPEED `= 54 (km)/(h) =((54 XX 1000)m)/( (3600)s )= 15 ms ^(-1)`

Discussion

694.	Two wires of equal length and different areas of cross section are kept parallel to each other and are connected to a battery as shown in the figure. A magnetic compass is placed exactly at the centre of the line joining the two wires in a plane perpendicular to the length of the two wires. what would be the direction of the north pole of the magnetic compass ?
Answer» Solution :The magnetic FIELD around a magnet is three DIMENSIONAL and the strength of the magnetic field at CERTAIN distance around the the magnetic is EQUAL.

Discussion

695.	The speed of light in. water is 2.25 xx 10^(8) ms^(-1). If the speed of light in vacuum is 3 xx 10^(8) ms^(-1), calculate the refractive index of water.
Answer» Solution :Given: Speed of light in water `( upsilon)= 2.25 XX 10^(8) MS^(-1)` Speed of light in vacuum (c ) `= 3 xx 10^(8) ms^(-1)` Solution: `mu =(c )/(upsilon) rArr = (3 xx 10^(8) ms^(-1))/(2.25 xx 10^(8) ms^(-1))` `therefore mu = 1.33`

Discussion

696.	For a uniformly retarded motion, the velocity-time graph is :
Answer» a curve a straight line PARALLEL to the time axis a straight line PERPENDICULAR to the time axis. a straight line inclined to the time axis. Solution :a straight line inclined to the time axis.

Discussion

697.	A piece of iron weighs 44.6 gf in air. If the density of iron is 8.9xx10^(3)kgm^(-3), find the weight of iron piece when immersed in water.
Answer» ANSWER :39.5 GM

Discussion

698.	A train moving with uniform speed covers a distance of 120 m in 2 s. Calculate : (i) the speed of the train, (ii) the time it will take to cover 240 m.
Answer» Solution :Given S= 120 m t=2 s (i) Speed of the train = `("Distance TRAVELLED" )/("TIME TAKEN ")` or U `= (120)/(2s ) = 60 m s^(-1)` (II) Time taken to cover 240 m distance `t= ("distance" )/("Speed") = (240m) /(60 m s^(-1))= 4 s `

Discussion

699.	Two cork piece of same size and mass are dipped in two beakers containing water and oil. One cork floats on water but another sink in oil. Why ?
Answer» Solution :The cork floast on WATER because the density of cork is less than the density of water and another cork SINKS in the OIL because the desnity of cork is more than the oil.

Discussion

700.	An athlete completes one round of a circular track of diameter 200 in 40 s. What will be the distance covered and the displacement at the end of 2 m and 20 s?
Answer» SOLUTION :Given : Diameter of circular track =200 m time of complete =40 s Formula : Circumference of the track = `d pi m` speed = DISTANCE /time Circumference of the track =` d. pi` =200 x 3.14 =628 m speed = `"628m"/"40s"=15.7 ms^(-1)` Distance covered in 2 min 20 s = speed x time =15.7 x 140 s In the given time athlete covers `3 1/2` ROUNDS =2198 m The final position of athlete is as shown in figure (A - INITIAL position, B-final position) `therefore` Displacement =diameter of the track =200 m

Discussion

Explore topic-wise InterviewSolutions in .

A farmer moves along the boundry of a square field of side 10M in 40s. What will be the magnitude of displacement of the farmer at the end of 2 minutes 20 seconds from his initial position?

What is radioactivity? What is the cause for natural radioactivity ?

Relative density of a substance is expressed by comparing the density of that substance with the density of:

A body of weight 10 N sinks in water. Weight of the water displaced is 2N. Which principle is related to this?

What is lactometer and hydrometer ?

What happens to speed, velocity, acceleration when an object moves in a circle with uniform speed?

A spring balance shows 100 gf reading when a metallic sphere is suspended from its hook. When the completely immersed in water, the reading shown by the balance is 75gf. The relative density of the material of the sphere is

Select conductors of electricity from the following : Copper wire, silk thread, pure water, acidulated water,human body, glass, mercury.

Examine the graph and answer the following question. Say whether the acceleration from O to A is uniform? What about from A to B?

A piece of brass weighs 175 gf in air and 150 gf when fully immersed in water. The density of water is 1.0gcm^(-3).(i) What is the volume of the brass piece ? (ii) Why does the brass piece weigh less in water?

A pendulum clock becomes

The unit of magnetical flux density is …………………….

Where does a body experience maximum weight on the earth? What is the reason?

What does the odometer of an automobile measure?

The kinetic energy of an object of mass, m moving with a velocity of 5m//s is 25J. What will be its kinetic energy when its velocity is double? What will be its Kinetic energy when its velocity is increased three times. When its velocity is increased three times.

How long will sound take to travel in (a) an iron rail and (b) air, both 3.3 km in length ? Take speed of sound in air to be 330 m s^(-1) and in iron to be 5280 m s^(-1).

The data regarding the motion of two different objects A and B are given in the following table : Examine them carefully and state whether the motion of the objects is uniform or non-uniform.

An object of weight 500 N sinks in water. Weight of water overflowed is 50 N. What is the weight of the object in water?

Usha swims in a 90 m long pool. She covers 180 m in one minute by swimming from one end to the other and back along the same straight path. Find the average speed and average velocity of Usha.

At what temperature the density of water is maximum? State its value.

Name the type of waves produced when a tuning fork is struck in air.

When a point source of light is kept near a plane mirror

What is responsible for the flow of current through (i) a metallic conductor, (ii) an electrolyte?

Three students A,B and C determined the volume of a solid by immersing it in water in the overflow cans set up The result obtained will be wrong for : (A) , (B) , (C) .

How much heat energy is required to change 2 kg of ice at 0^@C into water at 20^@C? (Specific latent heat of fusion of water = 3,34,000J/kg, Specific heat capacity of water =4200 JKg^(-1) K^(-1) )

If this body is allowed to fall freely, will there be anychange in the force experienced by the body?

Speed is a ____ quantity whereas velocity is a _____ quantity.

Complete the following sentence : A longitudinal wave is composed of compression and ……………………. .

Define amplitude, time period and frequency of sound wave.

When a piece of wood is suspended from the hook of a spring balance, it reads 70 gf. The wood is now lowered into water.What reading do you expect on the scale of spring balance?

Define 1 J of work.

An object is thrown vertically upwards with velocity of 20ms^(-1). At what height will its kinetic energy and potential energy be equal? (g=10ms^(-2))

A unit positive charge is moved along the circumfer-ence of a circle of radius, r with a -5muC charge at the centre at the centre of the circle. Then, the work done in the process is "______".

Assertion (A) : Maximum sunlight reaches earth's surface during the afternoon time. Reason (R) : Heat from the sun reaches earth's surface by radiation.

Pulley is the most commonly used simple machine to draw water from a well since (A) its mechanical advantage is greater than one (B) it changes the direction of application of effort and makes it convenient to draw water

What is the connection between electricity and magnetism?

Name the radiations which are absorbed by the green house gases in the earth's atmosphere.

Decribe the energy transformations that occur as the Earth orbits the sun in its ellipitcal orbit.

Constant speed oof a train is 54 kim h ^(-1). What is its speed in unit 'ms ^(-1).?

The speed of light in. water is 2.25 xx 10^(8) ms^(-1). If the speed of light in vacuum is 3 xx 10^(8) ms^(-1), calculate the refractive index of water.

For a uniformly retarded motion, the velocity-time graph is :

A piece of iron weighs 44.6 gf in air. If the density of iron is 8.9xx10^(3)kgm^(-3), find the weight of iron piece when immersed in water.

A train moving with uniform speed covers a distance of 120 m in 2 s. Calculate : (i) the speed of the train, (ii) the time it will take to cover 240 m.

Two cork piece of same size and mass are dipped in two beakers containing water and oil. One cork floats on water but another sink in oil. Why ?

An athlete completes one round of a circular track of diameter 200 in 40 s. What will be the distance covered and the displacement at the end of 2 m and 20 s?

Speed is a quantity whereas velocity is a _ quantity.