: for A:

Using the laws of conservation of linear momentum and energy the velocities of two bodies after perfectly elastic collision are given by

…….(i)

….(ii)

Where are the masses of two bodies and are the velocities of two bodies before collision

If then

Form (i) and (ii), we get

and

i.e., in perfectly elastic collision of two moving bodies of equal masses, the bodies merely exchange their velocities after collision. Thus, statement A is correct.

For B.

In Eqs. (i) and (ii)

If then

Thus statement B is wrong.