Physics: Rolling without slipping?

[*Leeyah*]

A thin-walled, hollow spherical shell of mass m and radius r starts from rest and rolls without slipping down the track. Points A and B are on a circular part of the track having radius R. The diameter of the shell is very small compared to h and R, and rolling friction is negligible.

Please go here for pic:
http://tinypic.com/view.php?pic=2pze0eb&s=3

1) What is the minimum height h for which this shell will make a complete loop-the-loop on the circular part of the track?

2) How hard does the track push on the shell at point B, which is at the same level as the center of the circle?

3) Suppose that the track had no friction and the shell was released from the same height h you found in part (1). Would it make a complete loop-the-loop?

4) In part (3), how hard does the track push on the shell at point A, the top of the circle?

5) How hard did the track push on the shell at point A in part (1)?

Express answers in terms of the variables m, R, & constants