A ball with moment of inertia mr2 rests on top of a fixed sphere. There is friction

A ball with moment of inertia ηmr2 rests on top of a fixed sphere. There is friction between the ball and the sphere. The ball is given an infinitesimal kick and rolls down without slipping. Assuming that r is much smaller than the radius of the sphere, at what point does the ball lose contact with the sphere? How does your answer change if the size of the ball is comparable to, or larger than, the size of the sphere? You may want to solve Problem 4.3 first, if you haven’t already done so.