A small solid sphere rolls without slipping along a track that ends in a vertical loop of radius R. The sphere is released from rest at a height h above the lowest point of the loop. What is the minimum value of h (measured from the lowest point) that allows the sphere to maintain contact with the track at the top of the loop?
a) 3.4R
b) 2.5R
c) 2.7R
d) 3.0R