Chapter 7, Problem 46P

46 * Work-energy bar charts for a person going downstairs and upstairs are shown in Figure P7.46. The bar charts show the average energy conversion across several steps. The system is the person, Earth, and the stairs. (a) What are the initial and final states in each case? (b) Describe and explain the similarities in the bar charts. (c) Describe the differences in the bar charts. How do these differences explain why we are less tired going downstairs? (d) How do you explain that when we walk upstairs $\left|\Delta U_{\text{th}}\right|>\left|\Delta U_{\text{ch}}\right|$, but when we walk downstairs $\left|\Delta U_{\text{th}}\right|>\left|\Delta U_{\text{ch}}\right|$? (Hint: Think about what happens to our shoes and the stairs when we go downstairs.)