1. The problem statement, all variables and given/known data The figure below shows a thin, uniform bar whose length is L and mass is M and a compact hard sphere whose mass is m. The system is supported by a frictionless horizontal surface. The sphere moves to the right with velocity , and strikes the bar at a distance 1/4L from the center of the bar. The collision is elastic, and following the collision the sphere is at rest. The rod is being rotated from its center. Find the value of the ratio m/M. 2. Relevant equations 1/2mv^2=1/2Iω^2 3. The attempt at a solution I know the collision is elastic, so kinetic energy is conserved. But I don't know exactly how find which mass ratios will make the collision elastic. I think I know inertia (1/12MR^2). But I'm basically stuck from there.