Solve: (a) The food energy equals so (b) The mechanical energy would be 20% of the results of part (a): 7.40. Set Up: Set 20% of the food energy (in joules) equal to the total work you do in raising the weight N times. Solve: For each arm raise, you do work equal to where Reflect: It is not reasonable to do this many repetitions in a single exercise session. 7.41. Set Up: Set 20% of the food energy (in joules) equal to the total work you do in jumping upward a distance of N times. Solve: The total time it would take is thus Reflect: This would be a very strenuous workout even for a very fit person. 7.42. Set Up: Use Setting and gives Solve: 7.43 Set Up: For part (a), Take and For part (b), use with and this gives Solve: (a) (b) The final kinetic energy of each kilogram is equal to the initial potential energy, while the corresponding speed is By comparison, for a 70 kg person, (c) To double double since mg is constant, this means h must be doubled. You therefore need To double you must increase
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