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

[NinjaChachi]

Homework Statement

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?

Homework Equations

None of these are positive but:
KE=.5mv^2
F_av=m(Δv)/(Δt)

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 KE_f=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 F_av but didn't get the right answer (381N). What do I do?

 

[Doc Al]

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.

Good.

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?

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

 

[NinjaChachi]

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

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?

 

[Doc Al]

No I didn't use gravity. I just used 3.3-2.33 and tried 2.33-3.3.

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

How would I take gravity into account?

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