# Showing momentum will be conserved in moving reference frame

1. Sep 2, 2008

### briteliner

1. The problem statement, all variables and given/known data
the question gives me the masses and initial velocities of two balls which collide elastically and asks me to prove that it the momentum will be conserved in both a still reference frame and a moving one.

2. Relevant equations

3. The attempt at a solution
i know that the momentum will be conserved in the moving frame because the final velocities will account for the change in the initial once due to the added velocity, however i don't know how to prove this without being given the final velocities.

2. Sep 2, 2008

### briteliner

oh do i need to use lorentz transformations?

3. Sep 2, 2008

### Staff: Mentor

You have the initial and final velocities of everything in one frame (or you can figure them out). Transform those to the moving frame and see if things are still conserved. (I'd use Galilean transformations.)

4. Sep 2, 2008

### briteliner

I don't have the final velocities in the still frame though so how am I supposed to convert them? And I wouldn't I have to be given one of the final velocies? I have two unknowns and 1 formula

5. Sep 2, 2008

### Staff: Mentor

You have two unknowns and two conservation principles.

6. Sep 2, 2008

### briteliner

you mean energy and momentum? wouldn't they both give me the same thing since they both use m and v?

7. Sep 2, 2008

### briteliner

nevermind i got it thanks a lot