# Homework Help: Ball in Free Fall, Average Force Created on Impact (Bounce Up)

1. Feb 1, 2010

### leejqs

1. The problem statement, all variables and given/known data
After falling from rest at a height of 29.8 m, a 0.422 kg ball rebounds upward, reaching a height of 21.7 m. If the contact between ball and ground lasted 1.83 ms, what average force was exerted on the ball?

2. Relevant equations
Change in momentum (p) = Fnet* Change in Time
FGrav=m*g
Delta y = Vavg,y*Change in Time

3. The attempt at a solution
I understand all of these formulas, but I am not quite sure where the 1.83 ms goes as far as which time it is actually describing in a specific formula. I know that the average velocity on the way down is actually just the final velocity divided by 2, since the initial velocity is 0... I feel like I'm on the brink of solving this but I'm not quite sure where to go next..

Thanks!

2. Feb 1, 2010

### PhanthomJay

What is the velocity of the ball at impact, as it hits the ground? What is its velocity just as it leaves the ground on the rebound? You can use the kinematic equations applied to the ball in flight to get these values. Once you have found them, you can use your F_net=change in momnentum/change in time applied during the period of contact.