A man of mass M standing at a height h from the floor in a gravity free space throws a ball of mass m straight down with a speed u. When the ball reaches the floor, find the distance of the man above the floor.

Explanation

When the man throws the ball with velocity u, he recoils with velocity V.
mu = MV
`V=(mu)/(M)`
time taken by the ball to reach the ground `t=(h)/(u)` Distance moved by man in this time
`t=v.t=("mu")/(M).(h)/(u)=(m)/(M).h`
Height of man at the time the ball strikes the ground is `H=h+(m)/(M)h " " H=h(1+(m)/(M))`.