1. The problem statement, all variables and given/known data A billiard ball initially at rest is given a sharp impules by a cue. The cue is held horizontally at a distance h above the centre line as in figure. The ball leaves the cue with a speed v and eventually acquires a speed 9/7 v. Show that h=4R/5, where R is the radius of the ball 2. Relevant equations 3. The attempt at a solution The friction force acts in the direction of motion as angular velocity is greater than linear speed (backward slipping occurs). considering rotation about central axis, fR=I(alpha) where (alpha) is the angular acceleration. I can get 2 equations relating linear speed at time t and angular speed at time t. But I don't know how to relate impulse with speed of the ball. I also wanted to ask that if we consider rotation about the point of contact, there is no torque acting on the sphere. How do we proceed this way?