1. The problem statement, all variables and given/known data Ball A moving at 12m/s collides elastically with ball B as shown. If both balls have the same mass, what is the final velocity of ball A? ***theta = 60*** 2. Relevant equations Ui + Ki = Uf + Kf 3. The attempt at a solution I could only think of the above equation when I read elastic collision. However, the solution in the back of the book suggested using conservation of momentum, which I thought is only applicable to inelastic collision. The numerical answer is 6m/s which can be figure out using mv = mv and breaking it down to x and y components. I can see how they get to the numerical answer but I am lost as to why? Can someone please explain why I would use the formula for conservation of momentum? And also, I'm at a complete loss on how to approach a problem like this so can you also explain what I would need to solve the problem if it is an elastic collision? Thank you!