After falling from rest from a height of 35 m, a 0.49 kg ball rebounds upward, reaching a height of 25 m. If the contact between ball and ground lasted 1.7 ms, what average force was exerted on the ball?
Use the two heights to get the velocity before and after impact with the ground.
From those two velocities (in opposite directions) get the momentum change.
The average force is the momentum change during the bounce, divided by the contact time.