Q:

In my AP Physics class, we have had a class-wide debate over a physics problem for the last few days. The problem asked how much work it would take to move a satellite that was orbiting Earth at a certain height to a greater height. Some of us say that the work equals the change in potential energy, while others say that the work is the change in the total mechanical energy. The total energy method gives an answer of exactly half of the amount the potential energy method gives. Who is right?

- Samuel Levenson (age 18)

Charleston, WV, USA

- Samuel Levenson (age 18)

Charleston, WV, USA

A:

Think of energy conservation. That total mechanical energy change comes from somewhere. In this case, it's from the work done. So that's the answer. That there's a bigger increase in the potential energy, halfway balanced by a decrease in kinetic energy is an interesting fact (virial theorem) but it doesn't change the basic conservation law.

Mike W.

*(published on 03/04/2016)*