Motor cylist rides in the verticle circle in 'well of death' sphere of radius 9m. What will be speed required so that he does not lose contact at the highest point?

A motor cyclist wants to show a feat by going round on a verticle plane inside a spherical cage of radius 5m. What should be the minimum speed to avoid fall, if g is 9.8 m/s^2 ?

A small ball was released from rest from a point on a friction less track which ends in a loop in the form of a circle of radius 20 cm. What is the minimum verticle height of the point release so that the ball can remain in contact with the loop as it moves along it?