Question

A ball moving with a velocity v strikes a wall moving towards the ball with velocity u. An elastic impact lasts for t seconds. Find the mean elastic force acting on the ball

Answer 1

Relative speed of ball w.r.t wall is v+u

v+u

Therefore F=ChangeinmomentumtimeF=Changeinmomentumtime

=m[(u+v)−{−(v+u)}]t=m[(u+v)−{−(v+u)}]t

=2m(v+u)t