This problem was contributed to the Feynman Lectures Website by Sukumar Chandra.
A small solid rubber ball of radius r is thrown against a rough horizontal floor such that its velocity just before striking the floor at A is v making an angle of 60° with the horizontal and also has a back spin of angular velocity ω. It is observed that the ball bounces from A to B, then from B to A, then from A to B, etc. Assuming perfectly elastic impact determine
a) the required magnitude of ω of the back spin in terms of v and r.
b) the minimum magnitude of co-efficient of static friction,μs min, to enable this motion.
Answer :