An ice cube is placed on top of an overturned spherical bowl of radius r, as indicated in...

An ice cube is placed on top of an overturned spherical bowl of radius r, as indicated in Figure. If the ice cube slides downward from rest at the top of the bowl, at what angle θ does it separate from the bowl? In other words, at what angle does the normal force between the ice cube and the bowl go to zero?

FIGURE