Question

A ball moving with velocity v hits a massive wall moving towards the ball with a velocity u.An elastic impact lasts for time t

Answer 1

(0.5)mv^2 = KE

If the u and v are oppositely directed, then the final speed is (u+v) and the increase in energy can be calculated by the difference in KE from the above formula.

That is because speed of the two objects will always be equal to the separation speed of the two objects.

Otherwise, it’s a decrease in KE from (v-u)^2. (Note (u-v)^2 is the same value.)