CBSE Class 11 Physics Work Energy And Power Worksheet Set D

Question. A body of mass 10 kg at rest is acted upon simultaneously by two forces 4N and 3N at right angles to each other. The kinetic energy of the body at the end of 10 sec is:
a. 100 J
b. 300 J
c. 50 J
d. 125 J
Answer : D

Question. If the momentum of a body is increased by 100 %, then the percentage increase in the kinetic energy is:
a. 150 %
b. 200 %
c. 225 %
d. 300 %
Answer : D

Question. The potential energy of a body is given by A− Bx² (where x is the displacement). The magnitude of force acting on the particle is:
a. Constant
b. Proportional to x
c. Proportional to x²
d. Inversely proportional to x
Answer : D

Question. The potential energy of a system is represented in the first figure. The force acting on the system will be represented by:

Answer : C

Question. A body of mass 2 kg is thrown upward with an energy 490 J. The height at which its kinetic energy would become half of its initial kinetic energy will be: [ g = 9.8m/ s² ]
a. 35 m
b. 25 m
c. 12.5 m
d. 10 m
Answer : C

Question. A body of mass 5 kg is moving with a momentum of 10 kg-m/s. A force of 0.2 N acts on it in the direction of motion of the body for 10 seconds. The increase in its kinetic energy is:
a. 2.8 J
b. 3.2 J
c. 3.8 J
d. 4.4 J
Answer : D

Question. A rod of mass m and length l is lying on a horizontal table. The work done in making it stand on one end will be:
a. mgl
b. mgl/2
c. mgl/4
d. 2mgl
Answer : B

Question. A particle moves in a potential region given by U = 8x² − 4x + 400 J. Its state of equilibrium will be:
a. x = 25m
b. x = 0.25m
c. x = 0.025m
d. x = 2.5m
Answer : B

Question. An unloaded bus and a loaded bus are both moving with the same kinetic energy. The mass of the latter is twice that of the former. Brakes are applied to both, so as to exert equal retarding force. If x₁ and x₂ be the distance covered by the two buses respectively before coming to a stop, then:
a. x₁ = x₂
b. 2x₁ = x₂
c. 4x₁ = x₂
d. 8x₁ = x₂
Answer : A

Question. A bus can be stopped by applying a retarding force F when it is moving with a speed v on a level road. The distance covered by it before coming to rest is s. If the load of the bus increases by 50% because of passengers, for the same speed and same retarding force, the distance covered by the bus to come to rest shall be:
a. 1.5 s
b. 2 s
c. 1 s
d. 2.5 s
Answer : A

Question. A vehicle is moving on a rough horizontal road with velocity v. The stopping distance will be directly proportional to:
a. √v
b. v
c. v²
d. v³
Answer : C

Question. Two stones each of mass 5kg fall on a wheel from a height of 10m. The wheel stirs 2kg water. The rise in temperature of water would be:
a. 2.6º C
b. 1.2º C
c. 0.32º C
d. 0.12º C
Answer : D

Question. A body is attached to the lower end of a vertical spiral spring and it is gradually lowered to its equilibrium position. This stretches the spring by a length x. If the same body attached to the same spring is allowed to fall suddenly, what would be the maximum stretching in this case?
a. x
b. 2x
c. 3x
d. x/2
Answer : B

Question. ₈₀Hg²⁰⁸ nucleus is bombarded by α-particles with velocity 107 m/s. If the α-particle is approaching the Hg nucleus head-on then the distance of closest approach will be:
a. 1.115 10 m⁻¹³
b. 11.15 10 m⁻¹³
c. 111.5 10 m⁻¹³
d. Zero
Answer : A

Question. A charged particle A moves directly towards another charged particle B. For the (A+B) system, the total momentum is P and the total energy is E:
a. P and E are conserved if both A and B are free to move
b. A is true only if A and B have similar charges
c. If B is fixed, E is conserved but not P
d. If B is fixed, neither E nor P is conserved
Answer : A, C

Question. A 2kg block is dropped from a height of 0.4 m on a spring of force constant K = 1960 Nm⁻¹
The maximum compression of the spring is:
a. 0.1 m
b. 0.2 m
c. 0.3 m
d. 0.4 m
Answer : A

Question. A bus weighing 100 quintals moves on a rough road with a constant speed of 72km/h. The friction of the road is 9% of its weight and that of air is 1% of its weight. What is the power of the engine? Take g = 10m/s²
a. 50 kW
b. 100 kW
c. 150 kW
d. 200 kW
Answer : D

Question. The mass of a bucket containing water is 10 kg. What is the work done in pulling up the bucket from a well of depth 10 m if water is pouring out at a uniform rate from a hole in it and there is loss of 2 kg of water from it while it reaches the top? (g = 10m / sec²)
a. 1000 J
b. 800 J
c. 900 J
d. 500 J
Answer : C

Question. n small balls each of mass m impinge elastically each second on a surface with velocity u. The force experienced by the surface will be:
a. mnu
b. 2 mnu
c. 4 mnu
d. (1/2)mnu
Answer : B

Question. A stone projected vertically upwards from the ground reaches a maximum height h. When it is at a height 3h/4 the ratio of its kinetic and potential energies is:
a. 3 : 4
b. 1 : 3
c. 4 : 3
d. 3 : 1
Answer : B

Question. A car of mass ‘m’ is driven with acceleration ‘a’ along a straight level road against a constant external resistive force ‘R’. When the velocity of the car is ‘v’, the rate at which the engine of the car is doing work will be:
a. Rv
b. mav
c. (R + ma) v
d. (ma − R) v
Answer : C

Question. A ball of mass m moving with velocity V, makes a head on elastic collision with a ball of the same mass moving with velocity 2V towards it. Taking direction of V as positive velocities of the two balls after collision are:
a. – V and 2V
b. 2V and –V
c. V and – 2V
d. – 2V and V
Answer : D

Question. A uniform chain of length L and mass M is lying on a smooth table and one third of its length is hanging vertically down over the edge of the table. If g is acceleration due to gravity, the work required to pull the hanging part on to the table is:
a. MgL
b. MgL/3
c. MgL/9
d. MgL/18
Answer : D

Question. A constant force F is applied on a body. The power (P) generated is related to the time elapsed (t) as:
a. 2 P ∝t
b. P ∝ t
c. P ∝ t
d. 3/ 2 P ∝ t
Answer : B

Question. Two equal masses are attached to the two ends of a spring of spring constant k. The masses are pulled out symmetrically to stretch the spring by a length x over its natural length. The work done by the spring on each mass is:
a. (1/2) kx²
b. -(1/2) kx²
c. (1/4) kx²
d. -(1/4) kx²
Answer : D

Question. A long spring is stretched by 2 cm, its potential energy is U. If the spring is stretched by 10 cm, the potential energy stored in it will be:
a. U/25
b. U/5
c. 5 U
d. 25 U
Answer : D

Question. A particle of mass ‘m’ moving with velocity ‘v’ collides inelastically with a stationary particle of mass '2m' . The speed of the system after collision will be:
a. v/2
b. 2v
c. v/3
d. 3v
Answer : C

Question. A bullet of mass m moving with velocity v strikes a block of mass M at rest and gets embeded into it. The kinetic energy of the composite block will be

Answer : A

Question. A wooden block of mass M is suspended by a cord and is at rest. A bullet of mass m, moving with a velocity v pierces through the block and comes out with a velocity v / 2 in the same direction. If there is no loss in kinetic energy, then upto what height the block will rise:
a. m² v² / 2M²g
b. m² v² / 8M²g
c. m² v² / 4Mg
d. m² v² / 2Mg
Answer : B

Question. A smooth sphere of mass M moving with velocity u directly collides elastically with another sphere of mass m at rest. After collision their final velocities are V and v respectively. The value of v is:
a. 2uM/m
b. 2um/M
c. 2u/1 + (m / M)
d. 2u/1 + (M / m)
Answer : C

Question. A body of mass 40 kg having velocity 4 m/s collides with another body of mass 60kg having velocity 2 m/s. If the collision is inelastic, then loss in kinetic energy will be:
a. 440 J
b. 392 J
c. 48 J
d. 144 J
Answer : C

Question. One sphere collides with another sphere of same mass at rest inelastically. If the value of coefficient of restitution is 1/2 the ratio of their speeds after collision shall be:
a. 1 : 2
b. 2 : 1
c. 1 : 3
d. 3 : 1
Answer : C

Question. Two blocks A and B each of mass m, are connected by a masseless spring of natural length L and spring constant k.
The blocks are initially resting on a smooth horizontal floor with the spring at its natural length as shown in figure.

Answer : B, D

Question. A particle moves with a velocity v 5iˆ - 3ˆj + 6kˆms^–1 under the influence of a constant force F = 10iˆ + 10 ˆj + 20kˆ N.
The instantaneous power applied to the particle is:
a. 200 J-s^–1
b. 40 J-s^–1
c. 140 J-s^–1
d. 170 J-s^–1
Answer : C

Question. A neutron having mass of 1.67 x 10 kg⁻²⁷ and moving at 10⁸ m/ s collides with a deutron at rest and sticks to it. If the mass of the deutron is 3.34 x 10 kg⁻²⁷ the speed of the combination is:
a. 2.56×10³ m/ s
b. 2.98×10⁵ m/ s
c. 3.33×10⁷ m/ s
d. 5.01×10⁹ m/ s
Answer : C

Question. A particle of mass m moving eastward with a speed v collides with another particle of the same mass moving northward with the same speed v. The two particles coalesce on collision. The new particle of mass 2m will move in the north-easterly direction with a velocity:
a. v / 2
b. 2v
c. v / √2
d. v
Answer : C

Question. A vehicle is drive along a straight horizontal track by a motor which exerts a constant driving force. The vehicle starts form rest at t = 0 and effects of friction and air resistance are negligible. If kinetic energy of vehicle at time t is E and power developed by the motor is P, which of the following graphs are correct?

Answer : A, C

Question. A stone is projected at time t = 0 with a speed V₀ and at an angleθ with the horizontal in a uniform gravitational field. The rate of work done (P) by the gravitational force plotted against time (t) will not be represented by which of the following graphs?

Answer : A, B, C

Question. Two men with weights in the ratio 5 : 3 run up a staircase in times in the ratio 11 : 9. The ratio of power of first to that of second is:
a. 15/11
b. 11/15
c. 11/9
d. 9/11
Answer : A

Question. The change of momentum in each ball of mass 60gm, moving in opposite directions with speeds 4m/ s collide and rebound with the same speed, is:
a. 0.98kg-m/ s
b. 0.73kg-m/ s
c. 0.48kg-m/ s
d. 0.22kg-m/ s
Answer : C

Question. A body falling from a height of 20m rebounds from hard floor. If it loses 20% energy in the impact, then coefficient of restitution is:
a. 0.89
b. 0.56
c. 0.23
d. 0.18
Answer : A

Question. A rubber ball is dropped from a height of 5 m on a planet where the acceleration due to gravity is not known. On bouncing, it rises to 1.8m. The ball loses its velocity on bouncing by a factor of:
a. 16/25
b. 2/5
c. 3/5
d. 9/25
Answer : C

Question. A body of mass M was slowly hauled up the rough hill by a force F which at each point was directed along a tangent to the hill. Work done by the force:

a. is independent of shape of trajectory
b. depends upon vertical component of displacement but in dependent of horizontal component
c. depends upon both the components
d. does not depend upon coefficient of friction
Answer : A, C

Question. A particle is projected form a point at an angle with the horizontal at t = 0.At an instant ‘t’, if p is linear momentum, x horizontal displacement, y is vertical displacement and E is kinetic energy of the particle, then which of the following graphs are correct?

Answer : ALL

Question. Two inclined frictionless tracks of different inclinations meet at A from where two blocks P and Q of different masses are allowed to slide down form rest at the same time, one on each track, as shown in figure. Then:

a. both blocks will reach the bottom at the same time
b. block Q will reach the bottom earlier than block P
c. both block reach the bottom with the same speed
d. block Q will reach the bottom with a higher speed than block P
Answer : B, C

 

SECTION – A CONCEPTUAL AND APPLICATION TYPE QUESTIONS

1. A body is moving at constant speed over a frictionless horizontal surface . What is the work done by gravitational force ?

2. 1. Does the work done in raising a suitcase on to a platform depend upon how fast it is raised up ?

3. 2. Is it possible that a body be in accelerated motion under a force acting on the body , yet no work is being done by the force ? Explain with an example.

4. 3. A light body and a heavy body have same kinetic energy . Which one has greater linear momentum ?

5. 4. How does KE of a body change if its momentum is doubled ? 

6. 5. Is work done by a non conservative force always negative ?Comment . 

7. 6. Can a body have momentum without energy ? 

8. Two masses one n times heavier than the other are dropped from same height . How dotheir momentum compare just before they hit the ground ?

9. A spring is cut into two halves .How is the spring constant of each half affected ? 

10. Two springs A and B are identical but A is harder than B . On which spring more work will be done if they are stretchedby same force ?

11. A lorry and a car with the same kinetic energy are brought to rest by the application of the brakes which provide equal retarding force . Which of them will come to rest in a shorter distance ?

12. What happens to the potential energy :
a) Two dissimilar charges are brought near each other
b) A body is taken away against the gravitational force .

13. Two coolies lift same load from the road to the roof of a bus . One of them takes 1 minute and the other takes 2 minutes to do the same job .who has done more work and whose power is more ?

14. Name the process in which
(i) Momentum is conserved but KE is not conserved ?
(ii) Momentum changes but KE does not change ?

15. Difference between conservative and non – conservative forces. 

16. Show that power is equal to dot product of force and velocity . 

17. What are head – on and oblique collisions ? 

18. Is total energy conserved in an inelastic collision ? 

19. Why does a pilot looping a vertical loop not fall down even at the highest point ?

SECTION – B NUMERICAL PROBLEMS

1. In a ballistics demonstration a police officer fires a bullet of mass 50 g with speed 200 m/s on a soft plywood of thickness 2 cm . The bullet emerges with only 10 % of its KE . What is the emergent speed of the bullet ?

2. A bullet of mass 50 g moving with velocity of 400 m/s strikes a wall and goes out from the other side with a velocity of 100 m/s . Calculate the work done in passing through the wall ?

3. The momentum of a body is increased by 100 % .What is the percentage increase in its KE ? 

4. A train of mass 2000 quintal is drawn up an inclined plane of 2 in 100 at the rate of 72 km/h.If the resistance due to friction is 3000 N , calculate the power of the engine .

5. 2. A ball is dropped from rest at a height of 12 m . If it loses 25 % of KE on striking the ground ,what is the height to which it bounces ?

6. 3. A mass of 2 kg attached to a spring is vibrated horizontally by displacing the mass 40 cm from its equilibrium position and releasing it . Find the maximum velocity of the mass .Spring constant is 24.5 N/m

7. 4. A pump on the ground floor of a building can pump up water to fill a tank of volume 30m³in 15 min . If the tank is 40 m above the ground , the efficiency of the pump is 30 % ,how much electric power is consumed by the pump ?

8. 5. A bullet of mass 0.012 kg and horizontal speed 70 m/s strikes a block of wood of mass 0.41 kg and instantly comes to rest with respect to the block. The block is suspended from the ceiling by means of thin wires . Calculate the height to which the block rises . Also estimate the amount of heat produced in the block.

9. A metal ball of mass 2 kg moving with speed of 36 km/h has a head on collision with a stationary ball of mass 3 kg . If after collision both the balls move as a single mass , what will be the loss in kinetic energy due to collision ?

10. If the kinetic energy of a body increases by 300 % , by what percent will the linear momentum of the body increase ?

11. A mass of 4 kg moving with 10 m/s comes to rest , after covering 2m on a horizontal surface . Calculate
(i)coefficient of kinetic friction between surfaces

(ii) workdone by frictional force
(iii)workdone by gravitational force.

12. A body of mass 2 kg is resting on a rough horizontal surface . A force of 20 N is now applied to it for 10 seconds , parallel to the surface . If the coefficient of kinetic friction between the surfaces in contact is 0.2 s , calculate
(i)workdone by the applied force in 10s
(ii)change in kinetic energy of the object in 10 s

13. A girl of mass 50 kg sits in a swing formed by a rope of 8m length. A person pulls the swing to a side so that the rope makes an angle of 60 ⁰ with the vertical .What is the gain in potential energy of the girl ?

14. A car of mass 1000 kg accelerates uniformly from rest to a velocity of 54 km/hr in 5 seconds. Calculate
(i)its acceleration
(ii)its gain in KE
(iii)average power of the engine during this period , neglect friction.

15. A molecule in a gas container hits a horizontal wall with speed 200 m/s and angle 30 ^o with the normal , and rebounds with the same speed .
(i)Is momentum conserved in the collision?
(ii)Is the collision elastic or inelastic ?

 

16. Two identical ball bearings in contact with each other and resting on a frictionless table are hit head – on by another ball bearing of the same mass moving initially with a speed v . If the collision is elastic , which of the situations shown ,is a possible result after collision ?

17. The bob of a pendulum isreleased from a horizontal position A as shown . If the length of the pendulum is 1.5 m , what is the speed with which the bob arrives at the lowermost point B , given that it dissipates 5 % of its initial energy against air resistance ?

18. A 1 kg block situated on a rough incline to a spring of spring constant 100 N/m as shown . The block is released from rest with the spring in the unstretched position The block moves 10 cm down the incline before coming to rest . Find the coefficient of friction between the block and the incline .Assume that the spring has negligible mass and the pulley is frictionless .

Please click on below link to download CBSE Class 11 Physics Work Energy And Power Worksheet Set D