# Momentum Problems New Student

1. Jan 9, 2007

### street

Hi. I just recently switched into a physics course midyear, and I really don't know whats going on. Help with a few of these questions would be greatly appreciated.

1. The problem statement, all variables and given/known data
A 2.5 kg ball strikes a wall at 8 m/s and rebounds at 7m/s. The ball is in contact with the wall for 0.2 seconds. What is the force on the wall?

2. Relevant equations
Im really not sure. Is this it?
F?t=?p

F(1)?t=m(1)v(1,f) - m(1)v(1,i)

F(2)?t=m(2)v(2,f) - m(2)v(2,i)

3. The attempt at a solution

I'm not sure how to apply that information into the equations, and I'm not even sure if the equations are right.

2. Jan 9, 2007

I don't see why you introduced all those 'initial' and 'final indices', since the only thing you have to know and apply here is that impulse equals change in momentum. You know the definition of impulse, and you know the initial and final (if you like it better) momentum.

3. Jan 9, 2007

### street

F∆t =∆p ?

I still don't understand how to do it.

4. Jan 9, 2007

### theperthvan

Yep. and ∆p=m∆v

So, F∆t=m∆v
Finding F... F= m∆v/∆t

5. Jan 9, 2007