You're at a shopping mall. If you stand still on the escalator, it takes 30 seconds for it to carry you up one floor, about 5 meters. But if you walk up, you get to the top of the escalator in only 15 seconds. A. How much work does the escalator do on you in lifting you up to the next floor, if you just stand there? That is, how much of your gain in potential energy comes from the escalator? B. And how much work does the escalator do on you if you walk up? C. Some people expect the answer in part B to be the same as in part A, saying that the escalator is still exerting the same force over the same distance; some people expect it to be more, saying that when you walk up your feet press down harder on the stairs than they do if you just stand, so the force is greater; and some people expect it should be less, saying that you're expending energy, so the escalator must expend less. So... explain the problem with the reasoning by the folks who have it wrong.