Energy is conventionally measured in Calories as well as in joules. One Calorie

Question

Energy is conventionally measured in Calories as well as in joules. One Calorie in nutrition is one kilocalorie, defined as 1 kcal = 4186 J. Metabolizing 1 g of fat can release 9.00 kcal. A student decides to try to lose weight by exercising. She plans to run up and down the stairs in a football stadium as fast as she can and as many times as necessary. Is this in itself a practical way to lose weight? To evaluate the program, suppose she runs up a flight of 80 steps, each 0.150 m high, in 59.5 s. For simplicity, ignore the energy she uses in coming down (which is small). Assume that a typical efficiency for human muscles is 20.0%. Therefore when your body converts 100 J from metabolizing fat, 20 J goes into doing mechanical work (here, climbing stairs). The remainder goes into extra internal energy. Assume that the student's mass is 65.0 kg.

How many times must she run the flight of stairs to lose 1 lb of fat?

Explanation / Answer

one pound is   453.92 grams . So the energy released when this amount of fat is burnedis    453.92 * 9.00 = 4085.26 kcal= .         = 17100915 Joules . Mechanical work running up steps = 65.0 * 9.80 * 80 * 0.15 =   7644 Joules . Fat energy burned running stairs = 38220 Joules . Number of times to run stairs = 17100915 /38220 =    447 times one pound is   453.92 grams . So the energy released when this amount of fat is burnedis    453.92 * 9.00 = 4085.26 kcal= .         = 17100915 Joules . Mechanical work running up steps = 65.0 * 9.80 * 80 * 0.15 =   7644 Joules . Fat energy burned running stairs = 38220 Joules . Number of times to run stairs = 17100915 /38220 =    447 times

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