# Collision Problem

1. Jun 8, 2005

### Jchem

A 12 kg block (A) is sliding right with a speed of 2.2 m/s collides with a 20 kg block (B) which is travelling left at 3.0 m/s.

After the collision the 12 Kg block is moving left at a speed of 1.6 m/s

a) what is the velocity of the 20 kg block after the collision?

b) The collision lasts for 0.025s, what is the average force experienced by the 12kg block?

For a) i just used:

P = mv

Pa + Pb = Pa' + Pb'

plugged in the numbers and got Vb' = .72 m/s left.

I'm having trouble with part b) .. any ideas on how i could get started?

thanks

2. Jun 8, 2005

### whozum

For part B), you need to consider the relationship between impulse and momentum (in terms of forces).

3. Jun 8, 2005

### Jchem

ok, well i know that impulse is the change in momentum.

I could find the change in momentum by subtracting Pa' from Pa.

So now I have the impulse

How do I come up with the average force? or is the impulse itself the average force?

4. Jun 8, 2005

### whozum

Force is the change in momentum per unit time.
Average force is the net change in momentum over the net change in time.

5. Jun 8, 2005

### Jchem

man i have to learn how to use these markup codes....

so I'm thinking that the average force can be found by using:

F = (m /\V)/(/\t)

Im using /\ for delta or "change in"

6. Jun 8, 2005

### whozum

That looks good to me.