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## Homework Statement

A mass is placed at the top of a frictionless incline track. The bottom of the track goes into a loop. At what minimum height does the block with mass m have to be released above the ground in order to reach point b (the top of the loop).

## Homework Equations

mg(h

_{min})=mv

_{b}

^{2}/2 +mg2R.

## The Attempt at a Solution

The above formula shows that the minimum height has to be 2R because v

_{b}=0. I understand that U

_{gravity}= mgh. But I don't understand why mv^2/2 was added on the right side. I am sitting here study my textbook and can't make sense of it.