# Homework Help: 2D Collision

1. Feb 13, 2008

### Littlepig

1. The problem statement, all variables and given/known data
Ok, I'm making an algorithm to calculate some stuff, and meanwhile, i needed to compute a 2D collision between 2 particles of same mass.

To work that out, I needed to change referential to Mcenter. The problem was there...

2. Relevant equations
Vcm=(v1+v2)/2 (m1=m2)
3. The attempt at a solution
ok, Vcm=(v1+v2)/2
so, v1cm=v1-Vcm=v1-(v1+v2)/2=(v1)/2-(v2)/2
in the same way:
v2cm=v2-Vcm=v2-(v1+v2)/2=(v2)/2-(v1)/2

Now, the problem is: this too equations are L. Dependent, that means the matrix related to it isn't invertible, so, after i calculate the Vfinal in CM referencial, i can't change it to lab referential.
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

2. Feb 13, 2008

### Staff: Mentor

Why not? Just do the reverse of what you did to get to the CM frame: Instead of subtracting (V1 + V2)/2, add it.

3. Feb 13, 2008

### Littlepig

ah, duh, yeah

Tks Doc Al