What Is the Maximum Force Exerted by the Floor on the Ball?

[julz3216]

Homework Statement

A 41 rubber ball is dropped from a height of 1.8 and rebounds to two-thirds of its initial height.
http://session.masteringphysics.com/problemAsset/1070447/4/09.P29.jpg
The figure (Part C figure) shows the impulse received from the floor. What maximum force does the floor exert on the ball?
t=5ms

Homework Equations

change in p = F*change in time
F=ma

The Attempt at a Solution

I tried and got Fmax = .176 by plugging into the 1st equation for impulse

 

[LowlyPion]

If you solved the other problem you posted you should know how to solve this so long as you calculated your Impulse correctly from the info given.

 

[julz3216]

So I tried to do F*change in t = change in m*v but it didn't work. i calculated velocity by doing change in d/ change in t. i used 2.5 for t because that is where fmax occurs and i also used d as 1.8 because that is the distance the ball travels in 2.5 seconds

so i got v=.72 and then mv=.029
so 2.5F = .029
F = .0116

and that was wrong. so i don't really know what to do?

 

[LowlyPion]

So I tried to do F*change in t = change in m*v but it didn't work. i calculated velocity by doing change in d/ change in t. i used 2.5 for t because that is where fmax occurs and i also used d as 1.8 because that is the distance the ball travels in 2.5 seconds

so i got v=.72 and then mv=.029
so 2.5F = .029
F = .0116

and that was wrong. so i don't really know what to do?

Where did you get v = .72 from? It fell 1.8m

V² = 2*9.8*1.8m

How fast does it bounce back?

Isn't that going to give you the ΔV that you want to use?

The 2.5 ms* Fmax looks ok though.