A small ball falling vertically downward with constant velocity 4 m/s strikes elastically a massive wedge moving with velocity 4 m/s horizontally as shown. The velocity of the rebound of the ball is
A ball A is falling vertically downwards with velocity v1. It strikes elastically with a wedge moving horizontally with velocity v2 as shown in figure. What must be the ratio so that the ball bounces back in vertically upwards direction relative to wedge?