## a ball being dropped and bouncing back up?

1. The problem statement, all variables and given/known data
After falling from rest at a height of 30m, a 0.50 kg ball rebounds upward, reaching a height of 20m. If the contact between ball and ground lasted 2.0 ms, what a average force was exerted on the ball?

2. Relevant equations
The kinematic equations?
F=ma
w=mg?
I dont really know

3. The attempt at a solution
Sorry I don't even know where to begin. I don't really understand this section in the book so i dont even know what to do. The answer is supposed to come out to 1.1 x 10^4 upward.
 PhysOrg.com science news on PhysOrg.com >> City-life changes blackbird personalities, study shows>> Origins of 'The Hoff' crab revealed (w/ Video)>> Older males make better fathers: Mature male beetles work harder, care less about female infidelity
 Recognitions: Homework Help Science Advisor You need to work out the speed the balls hits the floor and then the speed it starts backup at. Acceleration is just change in speed / time. Hint - the speed it starts back up is the same as the speed a ball dropped from the second height would reach the floor.
 Ok so the speed of the ball when it hits the ground first time would need the kinematic equation Vf^2= Vi^2 + 2ad right? Vf^2= (0)^2 + 2(9.8)(30) Vf^2 = 588 Vf~24.3 m/s ? Vf^2= 2(9.8)(20) Vf^2 = 392 Vf ~ 19.8 m/s ? I think thats correct. correct me if I'm wrong please. How do I find the acceleration?

Recognitions:
Homework Help

## a ball being dropped and bouncing back up?

Acceleration = change in velocity / time
Whats the total change in velocity (watch the signs!)
 Ohhh... So the acceleration is the change in velocity which would be 19.8 - 24.3/change in time. Then put it in the F=ma and solve for F correct? or is there more?
 Recognitions: Homework Help Science Advisor Correct method - but be careful of the signs.
 OK thank you very much. I was stuck on this problem for a while.

 Similar discussions for: a ball being dropped and bouncing back up? Thread Forum Replies Introductory Physics Homework 3 Introductory Physics Homework 2 Introductory Physics Homework 1 Computing & Technology 0 Introductory Physics Homework 14