1. The problem statement, all variables and given/known data A particle of mass m and initial velocity v0 collides elastically with a particle of unknown mass M coming from the opposite direction as shown in the left-hand sketch on the next page. After the collision, m has velocity v0/2 at right angles to the incident direction, and M moves off in the direction shown in the sketch. Find the ratio M/m. 2. Relevant equations None given, although I'd assume the elastic condition collision equations. 3. The attempt at a solution I don't even know where to begin.