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# Energy is conventionally measured in Calories

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 one gram 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 60 steps, each 0.12 m high, in 65 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%. This means that 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 the student's mass is 50.0 kg. (a) How many times must she run the flight of stairs to lose one pound of fat? (b) What is her average power output, in watts and in horsepower, as she is running up the stairs?

#### Solution Preview

Metabolizing one gram of fat can release 9.00 kcal.
One pound of fat = 454 grams = 4086 kcal (454*9)

a) To consume 4086 kcal or 4086*4186=17104 kJ, first calculate how much energy is used for 1 ...

#### Solution Summary

The solution provides a detailed and step-by-step explanation for the problem analyzing energy of a calorie.

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