Question

A ball of mass m moves towards a moving wall of infinite mass with a speed 'v' along the normal to the wall. The speed of the wall is 'u' toward the ball. The speed of the ball after elastic collision with wall is

• A. $u+v$ away from the wall
• B. $2u+v$ away from the wall
• C. $|u-v|$ away from the wall
• D. $|v-2u|$ away from the wall

Answer 1

The correct option is B $2u+v$ away from the wall

In the frame of wall, the ball moves towards it with speed $u+v$ and due to momentum conservation velocity after collision returns with velocity $u+v$ in the direction in which wall is moving.

So from the ground frame, the velocity of ball after collision with wall is $2u+v.$