A girl of mass 55 kg throws a ball of mass 0.80 kg against a wall. The ball strikes the wall horizontally with a speed of $25 \mathrm {~m} / \mathrm { s }$ and it bounces back with this same speed. The ball is in contact with the wall $0.050 \mathrm {~s} .$ What is the magnitude of the average force exerted on the wall by the ball?

Question

Quizplus · Accepted Answer

The change in momentum of the ball is:$$\Delta p = m v_f - m v_i = (0.80 \mathrm{~kg})(-25 \mathrm{~m/s} - 25 \mathrm{~m/s}) = -40 \mathrm{~kg \cdot m/s}$$The average force exerted on the wall by the ball is:$$F = \frac{\Delta p}{\Delta t} = \frac{-40 \mathrm{~kg \cdot m/s}}{0.050 \mathrm{~s}} = \boxed{800 \mathrm{~N}}$$

A Girl of Mass 55 Kg Throws a Ball of Mass