1. The problem statement, all variables and given/known data 2. Relevant equations 1/2m1v12 + 1/2m2v22 = 1/2m1v1f + 1/2m2v2f m1v1 + m2v2 = m1v1f + m2v2f v1 - v2 = -(v1f - v2f) 3. The attempt at a solution So I solved the momentum of conservation for the final velocity of object 1. I then plug that equation into the third equation listed above, as v1f. But the thing is the equation i get for v1f has v2f in it and that is what I am solving for and this is where I am stuck.