1. The problem statement, all variables and given/known data A rod of mass M is lying on a flat frictionless surface. A small ball of mass m and velocity v collides with the rod in the center at the rod at right angle to the rod. The collision is elastic. 2. Relevant equations a) Where is the axis of rotation for the rod after the collision? b) What is the angular velocity around the axis of rotation after this collision? c) What is the velocity of the center of mass of the rod after the collision? 3. The attempt at a solution As far as I can see, there should be no rotation. But how do I show this?