Ok, I have tried to work this out for about an hour now and I haven't gotten very far. In the question there are two equal masses. One of them is moving at a given velocity and the other is not moving at all. After the collision one disk goes off on a given angle while the other disk goes off on an angle perpendicular to that of the second disk. The question wants me to solve for the final velocities. So this is whats given: Mass one Mass two Initial velocity = 0 Initial velocity = vi1 Final velocity = ? Final velocity = ? Angle = 90-A2 (Not sure if thats right) Angle = A2 Mass = Mass two Mass = Mass one Oh ya and the collision is perfectly elastic. So I think I am supposed to have like 4 unknowns and then I am suposed to have 4 different equations. But the only equation I am aware of right now is vi1 = v1f + v2f This can be split up to two other equations like so: vi1x = v1fx + v2fx vi1y = v1fy + v2fy Ok, so I think thats right so far, then what I did was I made four other equations like so: v1fy = v1fy(sinA2-90) v1fx = v1fx(cosA2-90) v2fy = v2fy(sinA2) v2fx = v2fx(CosA2) Now I plugged those into the original two equations like so: v1ix = v1fx(cosA2-90) + v2fx(cosA2) v1iy = v1fy(sinA2-90) + v2fy(sinA2) Now this is where I am stuck. I am not sure if I am on the right track right now but I hit a dead end. I have too many unknowns and not enough equations. Either the answer is really easy and I just can't see it, or I messed up somewhere, or theres another equation I am supposed to use. But right now I am really stuck and would appreciate any help given.