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

The speed of the wall will not change after the collision. Let $v$  be the velocity of the ball after collision in the direction. Since collision is elastic $\left(e=1\right)$ . Speed of separation speed = Speed of approach Or $v-1=2+1orv=4m/s$