40048 + Interview Questions in Physics in Class 11

1.	An elevator can carry a maximum load of 1800 kg (elevator + passengers) is moving up with a constant speed of 2ms^(-1). The frictional force opposing the motion is 4000 N. Determine the minimum power delivered by the motor to the elevator in watts as well as in horse power.
Answer» Solution :The downward FORCE on the elevator is `F= MG+ F_(f)= (1800xx10)+ 4000= 22000N` The motor must supply enough power to balance this force. HENCE, `P= F*v= 22000xx2= 44000 W = 59 hp`.

Discussion

2.	Four particles each of mass 1 kg are at the four corners of a square of side Im. The M. of the system about a normal axis through centre of square is
Answer» `6KGM^(2)` `1.2kgm^(2)` `2kgm^(2)` `2.5kgm^(2)` ANSWER :C

Discussion

3.	A particle is rotating in a circle of radius R = (2)/(pi) m, with constant speed 1 mcdot s^(-1). Match the following two columns for the time interval when it completes (1)/(4) th of the circle.
Answer» ANSWER :i.D, II. B, iii. C, iv. B

Discussion

4.	Which of the following statements are true in the context of a compound microscope? (A) Each lens produces a virtual and inverted image (B) The objective has a very short focal length (C ) The eyepiece is used as a simple magnifying glass (D) The objective and eyepiece are convex and concave lenses respectively
Answer» (A) , (B) and (D) (B) and ( C) (A) (D) and ( C) (B) and (D) ANSWER :B

Discussion

5.	Two simple harmonic motions y_(1) =A sinomegat and y_(2) =A cos omegat are superimposed on a particle of mass m. Find the total mechanical energy of the particle.
Answer» Solution :Phase difference between the TWO SHMS is `90^(@)` THEREFORE, resultant amplitude is `A= sqrt(2A)E= (1)/(2)momega^(2)A_(R)^(2)= (1)/(2)momega^(2)(sqrt(2)A)^(2)= momega^(2)A^(2)`

Discussion

6.	In the above problem if we assume that gravity disappears instead of getting reversed, the body
Answer» CONTINUES to FALL down with UNIFORM velocity falls down with acceleration falls down & floats falls down with declaration Answer :A

Discussion

7.	A ring of radius R is first rotated with an angular velocity omega_(0) and then carefully placed on a rough horizontal surface. The coefficient of friction between the surface and the ring is mu. Time after which its angular speed in reduced to half is
Answer» `(omega_(0)MU R)/(2G)` `(omega_(0)mu R)/(2MU R)` `(2omega_(0)R)/(mu g)` `(omega_(0)R)/(2mu g)` Answer :D

Discussion

8.	A particle starts from rest and travels withconstant acceleration 'a' . After a time of 't_(0)' it 'sacceleration direction gets reversed . Identify correct options.
Answer» It's velocity when it returns BACK to initial point is `sqrt(2) a t_(0)` It's velocity when it returns back to initial point is `2 a t_(0)` TOTAL distance TRAVELLED by particle when it reaches back to initial point is `2 a t_(0)^(2)` Time taken to come back to initial point `(2+ sqrt(2)) t_(0)` Answer :A::C::D

Discussion

9.	Why do we wear white or light colour clothes in summer and dark colour clothes in winter ?
Answer» Solution :Substances of black colour ABSORB and emit the RADIATIONS better than light colour substances. Light colour clothes absorb less heat and reflect more heat coming from Sun in summer. Hence, less heat is FELT. Dark colour clothes absorb more heat hence out body can be warm in WINTER.

Discussion

10.	What is the largest average velocity of blood flow in an artery of radius 2 times 10^-3 m if the flow must remain laminar?(b) What is the corresponding flow rate?(take viscosity of blood to be 2.084 times 10^-3 Pa s)
Answer» SOLUTION :`0.98 ms^-1` (B) `1.24 TIMES 10^-5 m^3 s^-1`

Discussion

11.	A bolloon contains 400 m^(3) of hydrogens. If the mass of the balloon without hydrogen is 34kg. Its ne lifting is (Density of hydrogen 0.09 kg//m) Denstiy of air 1.3kg//m^(3))
Answer» `590 KG.wt` 450 kg.wt 70 kg. wt 36kg. Wt Answer :B

Discussion

12.	The error in measurement of side of a cube is 2%. Find the error in the volume of the cube?
Answer» SOLUTION :GIVEN, percentage error in SIDE length a is `(triangle a)/(a)xx100=2%` Volume of cube is, `V= a^(3)` Percentage error in volume of cube is : `(triangle V)/(V)xx100=3((triangle a)/(a))xx100= 3xx2%= 6%`

Discussion

13.	How will you distinguish between a hard boiled egg and a raw egg by spinning each on a table top
Answer» Solution :Same torque is applied to both `tau = I_(1) alpha_(1) = I_(2) alpha_(2)`Thus the angular acceleration is less, if moment of inertia is high. When raw EGG rotates the liquid matter moves AWAY from the AXIS and hence moment of inertia increases. So `alpha` decreases i.e., it comes to rest first Boiled egg BEHAVES as a rigid body and its pins more.

Discussion

14.	A gas is made up of hydrogen and oxygen molecules. Which molecule moves faster?
Answer» Solution :`v_(RMS) prop i/M`. So HYDROGEN molecule MOVES FASTER.

Discussion

15.	Can a body in liner motion be in equillibrium ?
Answer» SOLUTION :YES. The condition is that vector SUM of all forces acting on the body MUST be zero .

Discussion

16.	A bus is moving with a speed of 10m/son a straight road. A scooterist wishes to overtake the bus in 100 s. If the bus is at a distance of 1 km from the scooterist with what speed should the scooterist chase the bus?
Answer» `40 ms ^(-1)` `25ms^(-1)` `10 ms ^(-1)` `20 ms ^(-1)` Solution :SUPPOSE speed of SCOOTER is `v_(S)` and speed of bus is `v_(B),` the RELATIVE displacement between scooter & bus is, `X _(S) - x_(B) = ( x _(OS) -o_(OB)) + (v _(S) - v _(B))t ` When it overtakes `x _(S) -x_(B) =0` `therefore 0=100 0+ (v _(S) -10) t` `therefore (10 - v _(S))t = 1000` `therefore 10 -v _(S) = (1000)/(t)` ` therefore 10 -v _(S) = (1000)/(100)` `therefore v _(S) =20 m//s`

Discussion

17.	Two bodies have their moment of inertia I and 2I respectively about their axis of rotation. If their kinetic energies of rotation are equal, their angular momentum will be in the ratio :
Answer» `2:1` `1:2` `sqrt(2):1` `1:sqrt(2)` Solution :Rotational KINETIC energy `K=(1)/(2)Iomega^(2)` `=(1)/(2)(Iomega).OMEGA` `K=(1)/(2)L.omega` PUTTING `omega=(L)/(I)`, `K=(1)/(2)(L^(2))/(I)` `therefore L^(2)=2KI` `therefore L=sqrt(2KI)` Now for first body `L_(1)=sqrt(2K_(1)I_(1))` and for second body `L_(2)=sqrt(2K_(2)I_(2))` `therefore (L_(1))/(L_(2))=sqrt((2K_(1)I_(1))/(2K_(2)I_(2)))` Putting `K_(1)=K_(2)=KandI_(2)=2I,I_(1)=I` in EQU. `(L_(1))/(L_(2))=sqrt((KI)/(K(2I)))=sqrt((1)/(2))` `therefore (L_(1))/(L_(2))=(1)/(sqrt(2))` `therefore L_(1):L_(2)=1:sqrt(2)`

Discussion

18.	An elevator weighing 6000kg is pulled upward by a cable with an acceleration of 5 m//s^(-2). Taking g to be 10 ms^(-2), find the tension in the cable.
Answer» ANSWER :`90000 N`

Discussion

19.	A satellite is revolving around the earth in a circular oribt of radius r and velocity V_(0), A particle is projected from the satellite in forward direction with relative velocity V = (sqrt((7)/(6))-1)V_(0) the maximum distance from the centre during subsequent motion of the particle is
Answer» `(5R)/(3)` `(7R)/(5)` `(7r)/(4)` NONE Answer :B

Discussion

20.	Round off the following numbers to 3 significant figures (i) 23.63 m (ii) 40.47 kg (iiii) 0.05935m^(2) (iv) 0.009865m^(3)
Answer» Solution :(i) 23.6m (ii) 40.5 KG (iii) `0.0594 m^(2)` (iv) `0.00986 m^(3)`

Discussion

21.	The apparent wavelength of the light from a star, moving away from the earth, is 0.01% more than its real wave length. The speed of the star with respect to the earth is ……………… .
Answer» 10 km/s 15 km/s 30 km/s 60 km/s SOLUTION :`(v_(r))/(C) = (Delta LAMBDA)/(lambda)`or `v_(r) = (0.01)/(100) xx 3 xx 10^(8) = 3 xx 10^(4)` m/s = 30 km/s

Discussion

22.	The minimum deviation produced by a hollow prism filled with a certain liquid to be 30^@. The light ray is also formed to be refracted at angle 30^@ The refractive index of the liquid is
Answer» `SQRT2` `SQRT3` `SQRT(3/2)` `3/2` ANSWER :A

Discussion

23.	Two blocks A and B are pressed against a vertical wall by applying a horizontal force 'F' as shown in the figure. There is no friction between A and B. Then(a) Both the blocks A and B can be at rest for any magnitude of F (b) B can be at rest A moves down for smaller magnitude of F(c ) Both A and B will move down for smaller magnitude (d) A can be at rest and B moves down for larger magnitude of F
Answer» A and B are CORRECT C and d are correct a and d are correct b and c are correct Answer :B

Discussion

24.	A satellite in vacuum
Answer» is KEPT in ORBIT by solar ENERGY previous energy from GRAVITATIONAL field is kept in an orbit by remote control does not require any energy for revolving ANSWER :D

Discussion

25.	A hunterhas a machine gunthat can fire 50 g bullets with a velocityof150ms^(-1). A 60 kg tiger springs at him with a velocity 10ms^(-1) how many bullets must the hunter fire in tothe tiger in order to stop him in his track
Answer» Solution :Given: mass of bullet `m=50g = 0.5 kg` Velocityof bullet M= 60 kg VELOCITYV= 10`MS^(-1)` Let nbe thenumber of bulletrequiredto bepumped intotigerto stophim in histrack Accordingto the law of conservation ofmomentum MAGNITUDEOF themomentumof nbullets= magnitudeof tehmomentumof tiger of`nxxmv = Mv` or `n = (MV)/(mv) = (60 xx 10)/( 0.05 xx 150) = 80` `tan theta= (5)/(6)` `theta= tan ^(-1) ((5)/(6))= tan ^(-1)(0.8333)` `=39 .8^(@)`

Discussion

26.	The negative of the work done 'by the conservative internal forces on a system equals the change in:
Answer» TOTAL energy kinetic energy potential energy none of these Answer :C

Discussion

27.	If the average velocity of a body moving with uniform acceleration under the action of a force is ''v'' and the impulse it receives during a displacement of ''s'' is ''I'', the constant force acting on the body is given by
Answer» `(Ixxv)/(2S)` `(2Ixxv)/(s)` `(Ixxv)/(s)` `(Ixxs)/(V)` SOLUTION :`J=Fxxt, t=(s)/(v)`

Discussion

28.	(A): A man is on the northern bank of a river. To cross the river in a shortest time he should swim due south. (R) : Man should move opposite to the river flow to cross in shortest time.
Answer» Both (A) and (R) are TRUE and (R) is the correct explanation of (A) Both (A) and (R) are true and (R) is not the correct explanation of (A) (A) is true but (R) is FALSE (A) is false but (R) is true Answer :C

Discussion

29.	A tyre has air pumped at a pressure of 4 atmosphere at the room temperature 27^(@)C. If the tyre bursts suddenly calculate the final temperature. gamma =1.4
Answer» SOLUTION :`T _(2) =T_(1) (P_(2) //P_(1))^(1- (1//gamma)) = 300 (1//3) ^(1- (1//1.4)) = 300 (1//3) ^( 2//7) = 219.18 K`

Discussion

30.	A cat is able to land on its feet after a fall. Why?
Answer» Solution :When a cat falls to GROUND from a height, it STRETCHES its body alogn with the tail so that its MOMENT of inertia becomes high. Since`1omega` is to remain constant, the VALUE of angular speed `omegas` DECREASES and therefore the cat is able to land on the groundgently.

Discussion

31.	A block (A) of mass 3 kg in contact with a second block (B) of mass 2 kg rests on a frictionless horizontal surface. A horizontal force of 20 N is applied to push the block A. What is the force with which the block A pushes the block B?
Answer» 4N 6N 8N 10N Solution :The force of 20N producesan acceleration (a) in the two blocks and `a=(F)/(m_(1)+m_(2))= (20)/(3+2)= 4m//s^(2)` `therefore` The force with WHICHTHE block A PUSHES the block B is `f_(1)= m_(2)XX a= 2xx4= 8N`

Discussion

32.	A rectangular film of liquid is extended from 4cmxx2cm"to" 5cmxx4cm If the work done is 3xx10^(-4)J , the value of the surfacetension of the liquid is …..
Answer» `0.2Nm^(-1)` `8.0Nm^(-1)` `0.250Nm^(-1)` `0.125Nm^(-1)` Solution :FILM has two free surfaces , `thereforeDeltaA=2[(5xx4)xx10^(-4)-(4xx2)xx10^(-4))]` `=2[20xx10^(-4)-8XX10^(-4)]` `=2xxx12xx10^(-4)` `=24xx10^(-4)m^(2)` `therefore` Work `W=2TDeltaA` `3xx10^(-4)=24xx10^(4)xxT` `thereforeT=(3xx10^(-4))/(24xx10^(-4))` `thereforeT=(1)/(8)` `thereforeT=0.125Nm^(-1)`

Discussion

33.	Retardation means that acceleration :
Answer» DECREASES with TIME INCREASES with time increases and decreases decreases and increases Answer :A

Discussion

34.	Two racing cars of masses m_(1)and m_(2) are moving in circles of radii r_(1) and r_2 respectively. Their speeds are such that each makes a complete circle in the same time t. The ratio of the angular speed of the first to the second car is
Answer» `r_(1) : r_(2)` `m_(1) : m_(2)` `1:1` `m_(1)m_(2) : r_(1)r_(2)` ANSWER :C

Discussion

35.	Consider an object of mass 50 kg at rest on the floor. A Force of 5 N is applied on the object but it does not move. What is the frictional force that acts on the object?
Answer» SOLUTION :When the object is at rest, the external force and the static FRICTIONAL force are equal and OPPOSITE. The magnitudes of these TWO forces are equal,`f_s = F_(EXT)` Therefore, the static frictional force acting on the object is `f_s = 5N` The direction of this frictional force is opposite to the direction of `F_(ext)`

Discussion

36.	If a small part separates from an orbiting satellite, the part will
Answer» fall to the earth directly MOVE in a spiral and REACH the earth after a few rotations continue to move in the same orbit as the SATELLITE move farther AWAY from the earth gradually Answer :C

Discussion

37.	Let in_0 denote the dimensional formula of the permittivity of vaccum. If M = mass, L l= length , T = time and A = electric current, then
Answer» `in_0 = M^(-1) L^(2) T^(-1) A` `e_(0) = M^(-1) L^(-3) T^(2) A` `in_0 = M^(-1) L^(-3) T^(4) A^(2)` `in_0 = M^(-1) L^(2) T^(-1) A^(-2)` ANSWER :C

Discussion

38.	A small metal ball falls vertically and strickes a smooth plane inclined at an angle theta to the horizontal (theta lt 45^(@)). The ball rebounds horizontally. Show that a fraction (l-e) of the kinetic energy is lost during the impact and that if m is the mass and mu the speed of the ball before impact, the impulse on the plane is mu sec theta. Here e isi the coefficient of restitutuon.
Answer» ANSWER :N//a

Discussion

39.	In the arrangement shown in fig the mass of the ball 1 is eta=1.8 times as great as that of rod 2 The length of the later is l=100 cm The masses of the pulleys and the threads as well as the friction are negligible The ball is set on the same level as the lower end of the rod and then released How soon will the ball be opposite to the other end of the rod
Answer» Solution :Let the acceleration of the mass `m_(1)` is a upward, then the acceleration of `m_(2)` will be 2a downward From FBD we have `T-m_(1)g=m_(1)a` …(i) `m_(2)g-T' = m_(2)(2a)` …(ii) and `T=2T'` …(iii) Solving above equations we get `a=[(2m_(2)-m_(1)]/(m_(1)+4m_(2))]g` Given `m_(1)=1.8m_(2)` `:. a=g/29m//s^(2)` Acceleration of rod relative to ball `=2a-(-a)=3a` Displacement `l=100 CM =1m` By SECOND equation of motion, we have `l=ut+1/2(3a)t^(2)` or `1=0+1/2 3xxg/29 xxt^(2)` `:. t=1.40s`

Discussion

40.	(A): It is not possible for a system, unaided by an external agency to transfer heat from a body at lower temperature to another body at higher temperature. (R ): According to Clausius statement, "No process is possible whose sole result is the transfer of heat from a cooled object to a hotter object.
Answer» Both (A) and(R ) are true and (R ) is the CORRECT explanation of (A) Both (A) and (R ) are (R ) true and is not the correct explanation of (A) (A) is true but (R ) is FALSE Both (A) and (R ) are false Answer :A

Discussion

41.	Suppose the earth suddenly expends and its radius become 2R (R = radius of earth) keeping its mass same, then that will be the length of the day which at present is of 24 hours?
Answer» 1.5 hr 6 hr 96 hr 36 hr Solution :Here, `L_(1)=L_(2)` `I_(1)W_(1)=I_(2)W_(2)` `therefore (2)/(5)MR_(1)^(2)W_(1)=(2)/(5)MR_(2)^(2)W_(2)` `therefore R_(1)^(2)XX(2PI)/(T_(1))=R_(2)^(2)xx(2pi)/(T_(2))` `therefore (R_(1)^(2))/(T_(1))=((2R_(1))^(2))/(T_(2))` `therefore (1)/(24)=(4)/(T_(2))` `therefore T_(2)=96hr`

Discussion

42.	A sphere of mass 300 grams is rotated at uniform angular velocity 2rads^(-1) along a circle of radius 1.25 m in horizontal plane with help of light horizontal string. The tension in the string is
Answer» 0.25 N 1.5 N 2.5N 5N Answer :B

Discussion

43.	The equation to a transverse wave travelling in a rope is given by y=A cos(pi)/(2)[kx-omega-alpha] where A=0.6 m, k=0.005 cm^(-1),omega=8.0 s^(-1) and alpha is a non-vanishing constant. Then for this wave,
Answer» the wavelength of the wave is `lambda=8m` the maximum velocity `v_(m)` of a PARTICLE of the rope will be, `v_(m)=7.53 m//s`. the EQUATION of a wave which, when superposed with the given wave can produce standing waves in the rope is `y=A cos(pi)/(2)(kx+omega-alpha)` The equation of the wave can be represented by `y 2a cos(v)/(a)[t+(X)/(V)]` Solution :Given wave is `y=A cos.(pi)/(2)[kx-omega-alpha]` here wave number, `kxx(pi)/(2)=(2pi)/(lambda)` giving `lambda=(4)/(k)` here `k=0.005 cm^(-1)`. Hence `lambda=(4)/(0.005)cm=8m` maximum velocity `V_(m)=Axx` angular velocity. Here angular velocity `=(piomega)/(2)=(3.14xx8)/(2)=12.56 rad//s` hence `V_(m)=0.6xx12.56 m//s=7.53 m//s` ALSO, to produce STATIONARY waves, the two waves should travel in opposite direction and have same frequency. the wave given by `y=A cos(pi)/(2)(kx+omegat-alpha)` fulfils this condition.

Discussion

44.	Calculate work done from the graph.
Answer» SOLUTION :WORK done = area of triangle (OAB) - area of rectangle (BCDE) `W=(1)/(2)xx20xx10-10xx5=50J`

Discussion

45.	Two bolcks A & B are connected by a spring of stiffness 512N//m and placed on a smooth horizontal surface. Initially the spring has its equilibrium length. The indicated velocities are imparted to A & B. Find the maximum extension in the spring?
Answer» Solution :USING centre of MASS frome of refrence, we can say that `(1)/(2)muv_(rel)^(2)=(1)/(2)kx^(2)` [Here `mu=(m_(1)m_(2))/(m_(1)+m_(2))` (REDUCED mass)] `rArr((3xx6)/(3+6))(1.8+2.2)^(2)=512x^(2)` `rArr(2)(4)^(2)=512x^(2)` `rArrx=(1)/(4)m=25m`

Discussion

46.	A truck of mass 1200kg is moving with a speed of 7ms^(-1) when it collides with a second truck of mass 1600kg which is stationary. If the two trucks are automatically coupled together on impact, the speed with which combination moves is
Answer» 2 m/s 3 m/s 1.5 m/s 6 m/s Answer :B

Discussion

47.	A particle P is moving in a circle of radius a with a uniform speed u, C is the centre of the circle and AB is a diameter. The angular velocities of P about A and C are in the ratio
Answer» `1:1` `1:2` `2:1` `4:1` Solution :From the property of a circle, if an arc subtend an angle `theta` at any point A on CIRCUMFERENCE, then it will subtend an angle `2 theta` at CENTRE C. So in the same time interval a particle rotating in a circle TURN double the angle with respect to centre point C compared to point A. `:. omega_(c)=2 omega_(A)`.

Discussion

48.	The minimum force required to move a body up an inclined plane is three times the minimum force required to prevent it from sliding down the plane. If co-efficient of friction between the body and inclined plane is (1)/(2sqrt(3)), the angle of inclined plane is
Answer» `60^(@)` `45^(@)` `30^(@)` `15^(@)` ANSWER :C

Discussion

49.	Momentum is product of velocity and magnitude of velocity”. True or False ?
Answer» SOLUTION :Falsemomentumisproducy of MASS andvelocity

Discussion

50.	Oxygen boils at -183^(@)C. This temperature in Fahrenheit scale is …….. .
Answer» `-215.7^(@)` `-297.4^(@)` `-310.6^(@)` `-373.2^(@)` Solution :`(F-32)/(9)=(C )/(5)rArr F =32+(9)/(5)(-183)rArr F=-297.4^(@)F`

Discussion

Explore topic-wise InterviewSolutions in Current Affairs.

An elevator can carry a maximum load of 1800 kg (elevator + passengers) is moving up with a constant speed of 2ms^(-1). The frictional force opposing the motion is 4000 N. Determine the minimum power delivered by the motor to the elevator in watts as well as in horse power.

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A hunterhas a machine gunthat can fire 50 g bullets with a velocityof150ms^(-1). A 60 kg tiger springs at him with a velocity 10ms^(-1) how many bullets must the hunter fire in tothe tiger in order to stop him in his track

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If the average velocity of a body moving with uniform acceleration under the action of a force is ''v'' and the impulse it receives during a displacement of ''s'' is ''I'', the constant force acting on the body is given by

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Two bolcks A & B are connected by a spring of stiffness 512N//m and placed on a smooth horizontal surface. Initially the spring has its equilibrium length. The indicated velocities are imparted to A & B. Find the maximum extension in the spring?

A truck of mass 1200kg is moving with a speed of 7ms^(-1) when it collides with a second truck of mass 1600kg which is stationary. If the two trucks are automatically coupled together on impact, the speed with which combination moves is

A particle P is moving in a circle of radius a with a uniform speed u, C is the centre of the circle and AB is a diameter. The angular velocities of P about A and C are in the ratio

The minimum force required to move a body up an inclined plane is three times the minimum force required to prevent it from sliding down the plane. If co-efficient of friction between the body and inclined plane is (1)/(2sqrt(3)), the angle of inclined plane is

Momentum is product of velocity and magnitude of velocity”. True or False ?

Oxygen boils at -183^(@)C. This temperature in Fahrenheit scale is …….. .