### Force Motion and Energy

19.

The Rate of Change of Momentum is equal to its

Answer : C. Force applied on the object

20.

Look at the following statements
I. If work is to be done, a force must be exerted on the body
II. The force must produce motion or displacement
III. The force may or may not displace the body
IV. Work done is more when the force is given perpendicularly to the direction of motion of the body

Answer : B. I and II are correct

21.

A body is said to be moving with a uniform acceleration when its

Answer : A. velocity changes at a uniform rate

22.

Consider the following statements:
Assertion (A) : An athelete runs some distance before taking a long jump.
Reason (R ): It helps him to apply a large force

Answer : A. A is true , but R is false ( he runs some distance to gain momentum because it helps in jumping higher and longer because of inertia of motion gained due to the motion. He cannot apply large force in running)

23.

The force by which a body is attracted towards the centre of the earth is called