posted by Ashley .
A tennis ball of mass 0.057 kg is served. It strikes the ground with a velocity of 54 m/s (120 mph) at an angle of 21° below the horizontal. Just after the bounce it is moving at 51 m/s at an angle of 19° above the horizontal. If the interaction with the ground lasts 0.064 s, what average force did the ground exert on the ball?