# Magnitude of the average force exerted by ground on a ball.

1. Oct 8, 2015

### NinjaChachi

1. The problem statement, all variables and given/known data
Just before hitting the ground, a partially inflated 0.625kg basketball has a speed of 3.30m/s. Then it loses half of its kinetic energy as it bounces. (A)What is the ball's speed immediately after it bounces?(B) If the ball is in contact with the ground for 9.25ms, what is the magnitude of the average force exerted by the ground on the ball?

2. Relevant equations
None of these are positive but:
KE=.5mv^2
Fav=m(Δv)/(Δt)
3. The attempt at a solution
I found part A I believe. I just found the initial KE in that being KE=.5(.625)(3.30)^2 and got KE0=3.4
then it loses half so KEf=1.7 so to find the velocity I set up 1.7=.5(.625)v^2 and found the final velocity to be 2.33m/s.

I am quite confused on part B. I have tried m(Δv)/(Δt) to find the Fav but didn't get the right answer (381N). What do I do?

2. Oct 8, 2015

### Staff: Mentor

Good.

What did you use for Δv? Did you take gravity into account?

3. Oct 8, 2015

### NinjaChachi

No I didn't use gravity. I just used 3.3-2.33 and tried 2.33-3.3. How would I take gravity into account?

4. Oct 8, 2015

### Staff: Mentor

Try that again. Realize that the final and initial velocities have different directions.

Realize that m(Δv)/(Δt) will give you the average net force. What forces act on the ball during the collision with the ground?