Calculating Impulse and Average Force for a Ball Dropped on a Floor

[iamkristing]

[SOLVED] collision and impulse

Homework Statement

A 1.0 kg ball drops vertically onto a floor, hitting with a speed of 20 m/s. It rebounds with an initial speed of 5 m/s.
(a) What impulse acts on the ball during the contact?
kg·m/s

(b) If the ball is in contact with the floor for 0.020 s, what is the average force exerted on the floor?
N

Homework Equations

p=m*v
deltap=J
F=m(deltav)/deltat

The Attempt at a Solution

For (a) i used p=m*v and deltap=J

so I got (1*-20)-(1*5)=-25

and for (b) i used that F=(m*deltav)/deltat

which came out to be... 1(-25)/.020=0.5 N

both answers were wrong and I'm not sure what is wrong with the formulas I used...

Any help is appreciated! Thanks!

 

[mikelepore]

25/0.020=1250

 

[kamerling]

For a) the impulse is P_after - P_before and not P_before - P_after.

For b) see The reply of Mikelepore. I think you need to add the force of gravity as well.