Hi there, I am dealing with an inelastic, collinear momentum exchange of the form: m1v1+m2v2=m1u1+m2u2 where m1 & m2 are known. v1 & v2 are both 0 u1 & u2 are both unknown, however MOD(u1)+MOD(u2) is known (ie the sum of modulus of each speed, I don't know how to do straight brackets here.........) which initial speed is regarded as + or - is irrelevant (to me). I know that the exact speeds for u1 & u2 can be calculated, but I can't quite get me head around how (I'm more used to knowing one or the other, not their sum). Although I can find the answer by gradually increasing one of the values on a spreadsheet, I'd like to see the actual solution. I'm guessing it can be solved either simultaneously or with a bit of calculus, but I'm not very good and working these things out. Any help would be much appreciated. p.s. I know this looks like homework, but its not. It really does though doesn't it. Real world though, honest.