Chapter 7, Problem 7CQ

In Example 7.7, we calculated the final speed of a roller coaster that descended 20m in height and had an initial speed of 5 m/s downhill. Suppose the roller coaster had had an initial speed of 5 m/s uphill instead, and it coasted uphill, stopped, and then rolled back down to a final point 20m below the start. We would find that case that it had the same final speed. Explain in terms of conservation of energy.