CBSE Class 11 Work Energy and Power Worksheet C

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Question. In figure, a carriage P is pulled up from A to B. The relevant coefficient of friction is 0.40. The work done will be 

(a) 10 kJ
(b) 23 kJ
(c) 25 kJ
(d) 28 kJ

Answer: B

Question. A neutron with velocity v strikes a stationary deuterium atom, its K.E. changes by a factor of
(a) 15/16
(b) 1/2
(c) 2/1
(d) None of these

Answer: D

Question. If the linear momentum is increased by 5%, the kinetic energy will increase by
(a) 50%
(b) 100%
(c) 125%
(d) 10%

Answer: D

Question. A cord is used to lower vertically a block of mass M, through a distance d at a constant downward acceleration of g/8. Then the work done by the cord on the block is
(a) Mg d/8
(b) 3 Mg d/8
(c) Mg d
(d) – 7 mg d/8

Answer: D

Question. A force F̅ = (5î + 3ĵ + 2k̂) N is applied over a particle which displaces it from its origin to the point r̅ = (2î - ĵ)m. The work done on the particle in joule is
(a) +10
(b) +7
(c) –7
(d) +13

Answer: B

Question. In case of elastic collision, at the time of impact.
(a) total K.E. of colliding bodies is conserved.
(b) total K.E. of colliding bodies increases
(c) total K.E. of colliding bodies decreases
(d) total momentum of colliding bodies decreases.

Answer: C

Question. When the kinetic energy of a body is increased to three times, then the momentum increases
(a) 6 times
(b) 1.732 times
(c) 2 times
(d) 2 times

Answer: B

Question. A body moves a distance of 10 m along a straight line under the action of a force of 5 newtons. If the work done is 25 joules, the angle which the force makes with the direction of motion of body is
(a) 0º
(b) 30º
(c) 60º
(d) 90º

Answer: C

Question. A body of mass 5 kg initially at rest explodes into 3 fragments with mass ratio 3 : 1 : 1. Two of fragments each of mass ‘m’ are found to move with a speed 60 m/s in mutually perpendicular directions. The velocity of third fragment is
(a) 60 √2
(b) 20 √3
(c) 10 √2
(d) 20 √2

Answer: D

Question. Ten litre of water per second is lifted from a well through 10 m and delivered with a velocity of 10 ms^–1. If g = 10 ms^–2 , then the power of the motor is
(a) 1 kW
(b) 1.5 kW
(c) 2 kW
(d) 2.5 kW

Answer: B

Question. A nucleus ruptures into two nuclear parts which have their velocity ratio equal to 2 :1. The ratio of their respective nuclear sizes (nuclear radii )is
(a) 1 : 2
(b) 1: √2
(c) 1 : 2^1/3
(d) 1 : 8

Answer: C

Question. The rest energy of an electron is 0.511 MeV. The electron is accelerated from rest to a velocity 0.5 c. The change in its energy will be
(a) 0.026 MeV
(b) 0.051 MeV
(c) 0.08 MeV
(d) 0.105 MeV

Answer: C

Question. A one-ton car moves with a constant velocity of 15 ms^–1 on a rough horizontal road. The total resistance to the motion of the car is 12% of the weight of the car. The power required to keep the car moving with the same constant velocity of 15ms^–1 is [Take g = 10 ms^–2]
(a) 9 kW
(b) 18 kW
(c) 24 kW
(d) 36 kW

Answer: B

Question. Hail storms are observed to strike the surface of the frozen lake at 30⁰ with the vertical and rebound at 60⁰ with the vertical. Assume contact to be smooth, the coefficient of restitution is
(a) e = 1/√3
(b) e = 1/3
(c) e = √3
(d) e = 3

Answer: B

Question. A body starts from rest and acquires a velocity V in time T. The work done on the body in time t will be proportional to
(a) V/T t
(b) V²/T t²
(c) V²/T² t
(d) V²/T² t²

Answer: D

Question. When a U238 nucleus, originally at rest, decays by emitting an a-particle, say with speed of v m/sec, the recoil speed of the residual nucleus is (in m/sec.)
(a) – 4 v/234
(b) – 4 v/238
(c) 4 v/238
(d) – v/4

Answer: A

Question. A sphere of mass 8m collides elastically (in one dimension) with a block of mass 2m. If the initial energy of sphere is E. What is the final energy of sphere?
(a) 0.8 E
(b) 0.36 E
(c) 0.08 E
(d) 0.64 E

Answer: B

Question. A machine, which is 75% efficient, uses 12 J of energy in lifting up a 1 kg mass through a certain distance. The mass is then allowed to fall through that distance. The velocity at the end of its fall is (in m/s)
(a) √24
(b) √12
(c) √18
(d) √9

Answer: C

Question. A moving body with a mass m₁ and velocity u strikes a stationary body of mass m₂. The masses m₁ and m₂ should be in the ratio m₁/m₂ so as to decrease the velocity of the first body to 2u/3 and giving a velocity of u to m₂ assuming a perfectly elastic impact. Then the ratio m₁/m₂ is
(a) 5
(b) 1/ 5
(c) 1/ 25
(d) 25.

Answer: A

Question. A body is attached to the lower end of a vertical helical 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) 2 x
(c) 3 x
(d) x/2

Answer: B

Question. A bag of mass M hangs by a long thread and a bullet (mass m) comes horizontally with velocity V and gets caught in the bag. Then for the combined (bag + bullet) system
(a) momentum = mvM/M + m
(b) kinetic energy = mV²/2
(c) momentum = mV(M + m)/M
(d) kinetic energy = m² v²/2(M + m)

Answer: D

Question. A body of mass m moving with velocity v makes a head on elastic collision with another body of mass 2m which in initially at rest. The loss of kinetic energy of the colliding body (mass m ) is
(a) 1/2 of its initial kinetic energy
(b) 1/9 of its initial kinetic energy
(c) 8/9 of its initial kinetic energy
(d) 1/4 of its initial kinetic energy

Answer: C

Question. An automobile engine of mass M accelerates and a constant power p is applied by the engine. The instantaneous speed of the engine will be
(a) [Pt /M]^{1/ 2}
(b) [2Pt /M]^{1/ 2}
(c) [Pt / 2M]^{1/ 2}
(d) [Pt / 4M]^{1/ 2}

Answer: B

Question. A bullet fired into a fixed target loses half of its velocity after penetrating 3 cm. How much further it will penetrate before coming to rest assuming that it faces constant resistance to motion ?
(a) 2.0 cm
(b) 3.0 cm
(c) 1.0 cm
(d) 1.5 cm

Answer: C

Question. Given that a force F̅ acts on a body for time t, and displaces the body by ˆd . In which of the following cases, the speed of the body must not increase?
(a) F > d
(b) F < d
(c) Fˆ = dˆ
(d) Fˆ ⊥ dˆ

Answer: D

1. If two bodies stick together after collision will the collision be elastic or inelastic?

2. When an air bubble rises in water, what happens to its potential energy?

3. A spring is kept compressed by pressing its ends together lightly. It is then placed in a strong acid, and released. What happens to its stored potential energy?

4. A body is moving along Z – axis of a co – ordinate system is subjected to a constant force F is given by 

Where iˆ, j, kˆ are unit vector along the x, y and z – axis of the system respectively what is the work done by this force in moving the body a distance of 4m along the Z – axis?

5. A ball is dropped from the height h₁ and if rebounces to a height h₂. Find the value of coefficient of restitution?

6. State and prove work energy theorem analytically?

7. An object of mass 0.4kg moving with a velocity of 4m/s collides with another object of mass 0.6kg moving in same direction with a velocity of 2m/s. If the collision is perfectly inelastic, what is the loss of K.E. due to impact?

8. Prove that in an elastic collision in one dimension the relative velocity of approach before impact is equal to the relative velocity of separation after impact?

9. (a) Define potential energy. Give examples.

(b) Draw a graph showing variation of potential energy, kinetic energy and the total energy of a body freely falling on earth from a height h? 

Click on link below to download CBSE Class 11 Work Energy and Power Worksheet C.