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In Fig. 8-31, a small block of mass m = 0.032 kg can slide along the frictionless loop-the-loop, with loop radius R = 12cm. The block is released from rest at point P, at height h = 5.0R above the bottom of the loop. How much work does the gravitational force do on the block as the block travels from point P to (a) point Q and (b) the top of the loop? If the gravitational potential energy of the block-Earth system is taken to be zero at the bottom of the loop, what is that potential energy when the block is (c) at point P, (d) at point Q, and (e) at the top of the loop? (f) If, instead of merely being released, the block is given some initial speed downward along the track, do the answers to (a) through (e) increase, decrease, or remain the same?

I believe that the relevant equations are:

w=fd and w=mgh and maybe ke=1/2mv^2

Well I believe if I could figure out what the the specific heights at the given points are then I could make some calculations for instance: (a) If I new what the height at point Q was I would say the work would be mgh but I am having trouble understanding what they want me to do with the given height being 5.0R! Also, I believe the answer to (f) is remain the same right because work and PE don't have anything to do with velocity.

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# Homework Help: PE and KE problem

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