We put a very small coin right at the top of an object. This
object is a solid sphere. We assume such a coin is frictionless
(no friction with the object) and this object is fixed and has a
radius of R. We push this coin only very little bit and then it
falls by gravity. At what height below the starting point of this
coin will the coin be off the object (without touch with the
object)? Say the starting point is A and the detached point is
B, the question here asks the height difference between A
and B.
Hint 1: Energy conservation.
Hint 2: what is the normal force from the object to the coin?
Fig: 1