Question

I've tried this problem again and again using conservation of momentum and energy but I am not having any luck:

A ball of mass 0.300kg that is moving with a speed of 8.0m/s collides head-on and elastically with another ball initially at rest. Immediately after the collision, the incoming ball bounces backward with a speed of 3.1m/s .

a) Calculate the velocity of the target ball after the collision.

b) Calculate the mass of the target ball.

Please help and thank you!