2. Relevant equations
Tangential v = wr
3. The attempt at a solution
I first drew a force diagram for when the ball contacts the floor.
Topspin means the ball is moving tangentially backward.
Therefore, the bottom moves at v – wR. Friction works opposite in the direction of motion, so it will slow it down if v > wR, but it will speed it up if v < wR. Therefore, in order for there to be no change, v = wR, so w = v/R