Force of Friction
Assertion Reason
Type Questions
Read the following questions and choose:
- If both Assertion and Reason are true and the Reason is correct explanation of the Assertion.
- If both Assertion and Reason are true, but Reason is not correct explanation of the Assertion.
- If Assertion is true, but the Reason is false.
- If Assertion is false, but the Reason is true.
Question 37: Assertion: Two bodies of different masses have same momentum. Their kinetic energies are in the inverse ratio of their masses.
Reason: K.E. = 
Answer: (b)
Question 38: Assertion: Two bodies of different masses have same kinetic energies. Their momenta are in the direct ratio of their masses.
Reason: p = mv.
Answer: (d)
Question 39: Assertion: A gun of mass M fires a bullet of mass m, the ratio of recoil energy of gun to the K.E. of bullet is m/M.
Reason: In firing momentum is conserved. Kinetic energy is in the inverse ratio of masses.
Answer: (a)
Question 40: Assertion :
Work done by a force 
newton in displacing a body through 
is 16 joule.
Reason: 
= 16 joule.
Answer: (a)
Question 41: Assertion: Both a stretched spring and a compressed spring have potential energy.
Reason: Work is to be done against restoring force in each case.
Answer: (a)
Question 42: Assertion: Mass and energy are not conserved separately but are conserved as a single entity called `mass-energy equivalence'.
Reason: According to Einstein's special theory of relativity mass and energy are different manifestations of same and all related as E = mc2.
Answer: (a)
Question 43: Assertion: When a body is m oving uniformly in a circle, its momentum goes on changing continuously but its kinetic energy remains constant.
Reason: Momentum 
but K.E. 
In uniform circular motion 
changes but v2 does not change.
Answer: (a)
Question 44: Assertion: Work done by the gravitational force in moving a body through a certain distance remains the same whether the body moves uniformly or with decreasing acceleration.
Reason: Gravitational forces are conservative forces.
Answer: (b)
Question 45: Assertion: Kilowatt hour is the unit of electric power.
Reason: Watt hour has units of energy.
Answer: (d)
Question 46: Assertion: A weight lifter does no work in holding the weight up.
Reason: Work done is zero because distance moved is zero.
Answer: (a)
Question 47: Assertion: Work done in moving a body over a smooth inclined plane does not depend upon slope of inclined plane, provided its height is same.
Reason: W = mgh = mgl sin q
Answer: (a)
Question 48: Assertion: Linear momentum is conserved in both, elastic and inelastic collisions.
Reason: Total energy is conserved in all such collisions.
Answer: (b)
Matching Type Questions
Question: 49:
| Column - I | Column - II |
|---|---|
| Work done by pseudo forces | Zero word done |
| Uniform Circular Motion | Constant Kinetic Energy |
| Work done by frictional forces | Change in kinetic energy |
| Force at obtuse angle with displacement | Negative work |
Codes :
- I-C, II-A,B, III-C,D, IV-D
- I-A,B, II-A,C, III-C, IV-D
- I-C, II-B, III-D, IV-C
- I-A, II-C, B, III-D, IV-C, D
Answer: (a)
Question: 50.
| Column - I | Column - II |
|---|---|
| Work done by all forces | Change in potential energy |
| Work done by conservative force | Power |
| Work done per unit time | Energy |
| Capability of doing work | Change in kinetic energy |
Codes :
- I-D, II-A, III-C IV-B
- I-D, II-A, III-B, IV-C
- I-A, II-D, III-B, IV-C
- I-A, II-D, III-C, IV- B
Answer: (b)