# Homework Help: Perfectly elastic collision

1. Dec 2, 2008

### southernbelle

1. The problem statement, all variables and given/known data
In an isolated system, cart1 (with mass = 1 kg and vi1 = 2) has a perfectly elastic collision with cart2 (with mass = 2 kg and vi2 = 0). Find the velocity of cart1 and the velocity of cart2 after the collision.

2. Relevant equations
1/2m1vi12 + 1/2m2vi22 = 1/2m1v1f2 + 1/2m2v2f2

m1vi1 + m2v2i = m1v1f + m2v2f

3. The attempt at a solution

I plugged in all of the numbers.

For momentum I got
2= V1f + 2 V2f

For kinetic energy I got
4 = V1f2 + 2V2f2

Next I solved for V1f and plugged it into the equation.

I just need some confirmation that my answer is right.

It doesn't seem correct.

I got:
V2f = 2
V1f = -2

2. Dec 2, 2008

### Hootenanny

Staff Emeritus
You could check your answers yourself. Do they satisfy both the kinetic energy and momentum equations?

3. Dec 2, 2008

### southernbelle

No, they don't. You're right that was an easy way to check myself.