1. The problem statement, all variables and given/known data Assume that all particles are non-relativistic, that the target X is initially at rest, and that x has kinetic energy Tx in the laboratory frame. Show that the total kinetic energy of the reactants in the centre-of-mass frame is given by T* = μTx/mx, where mx is the mass of particle x and μ the reduced mass of x and X. Also obtain an expression for p* in terms of T* and μ. 2. Relevant equations I have completed the first part of this question without a problem. The second part, requiring p* to be found doesn't make sense to me. Surely the total momentum in the zero-momentum frame should be zero? Or is it expecting a different quantity? 3. The attempt at a solution First part done. Second part - don't know what it is asking.