1. The problem statement, all variables and given/known data We have two particles mass m called p1 and p2. P1 is stationary, p2 has energy E. They annihilate to produce to particles of mass 100m. We need to find the min value of E 2. Relevant equations 3. The attempt at a solution I suspect that the minimum initial energy of collision in the LAB frame is such that the CM frame energy is just enough to create the particles i.e that they are stat afterwards. In which case they would coalesce in the LAB frame (or any other). Is this true?