Physics: The Forces of Rolling?

Question

A solid brass ball of mass 0.280 g will roll smoothly along a loop-the-loop track when released from rest along the straight section. The circular loop has radius R = 14.0 cm, and the ball has radius r << R. (a) What is h if the ball is on the verge of leaving the track when it reaches the top of the loop? (b) If the ball is released at height h = 6.00R, what is the magnitude & direction of the horizontal force component acting on the ball at point Q?

Answer 1

Analyze the forces at the top of the loop:

The force of gravity pulling the ball downward,
the upward centrifigal force keeping the ball on the track,
and the force of the track pushing the ball downward.

The answer to the question is when the centrifigal force is exactly equal to the weight, so the force of the track equals zero.
mg=mw^2R
w is the angular velocity
w=sqrt(g/R)

Once you know the angular velocity, compute the equivalent linear velocity by mutlipying by R

then use mgh=1/2mv^2
to compute h

Where is point Q?

j