1. The problem statement, all variables and given/known data A question I had in an exam today, just wanted to see whether it was right: A ball is rolling down the inside of a concave surface. The radius of the ball and the curvature of the surface is such that there is no slide. Is work done by a) the friction force b) the Normal reaction force and c) the weight of the ball. 2. Relevant equations 3. The attempt at a solution Frictional force does no work, as the ball is rolling. The Weight of the ball does positive work (mg sin theta) The Normal reaction force does negative work (-mg sin theta) Does that sound right?