# 22. Energy is conventionally measured in Calories as well as inBIO joules. One Calorie in nutrition is one kilocalorie, definedas 1 kcal = 4 186 J. Metabolizing 1 g of fat can release9.00 kcal. A student decides to try to lose weight by exercis-ing. He plans to run up and down the stairs in a footballstadium as fast as he can and as many times as necessary.To evaluate the program, suppose he runs up a flight of80 steps, each 0.150 m high, in 65.0 s. For simplicity, ignorethe energy he uses in coming down (which is small). Assumea typical efficiency for human muscles is 20.0%. This state-ment means that when your body converts 100 J from metab-olizing fat, 20 J goes into doing mechanical work (here,climbing stairs). The remainder goes into extra internalenergy. Assume the student's mass is 75.0 kg. (a) How manytimes must the student run the flight of stairs to lose 1.00 kgof fat? (b) What is his average power output, in watts and inhorsepower, as he runs up the stairs? (c) Is this activity initself a practical way to lose weight?

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Step 1

Given:

Mass of the student = 75 kg

Height of one stair = 0.15 m

Number of stairs = 80

Time taken to climb the 80 stairs = 65 s

1 g fat burns and gives energy = 9 kcal

1 kcal = 4186 J

Step 2

(A) Calculating the number of times, the student must climb the stairs in order to lose 1 kg:

Step 3

(B) Calculating the aver...

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