Posted by **Jamie** on Thursday, January 4, 2007 at 6:51pm.

A small block of mass m can slide along the frictionless loop-the loop. The block is released from rest at point P, at height h =5R 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 (which has a height R) b) the top of the loop? If the gravitational poteintal 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?

a) The block is at potental enrgy then it goes to kinetic enrgy . so would i use mgh= 1/2mv^2?

b) I don't really get what to do here.

c)When the potential energy of the block is zero at the bottom of the loop whould this really make a difference in the answers to c), d) and e)? Wouldn't it be the same equation as above?

a/ Yes, but the mgh height is from the top starting point vertically to Q.

b. PE will be mgh where h is the vertical height from the bottom to the point. For instance, at the top of the loop, h is 2R, so gpe is 2mgr

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