A ball is moving with velocity `2m//s` towards a heavy wall moving towards the ball with speed `1m//s` as shown in figure. Assuming collision to be elastic, find the velocity of ball immediately after the collision.

Answer

D

Explanation

The speed of wall will not change after the collision. So, let v be the velocity of the ball after collision in the direction shown in figure.

Since, collision is elastic `(e=1)`.
separation speed=approach speed
or `v-1=2+1`
or `v=4m//s`