A 47-kg woman cheats on her diet and eats a 637-Calorie (637 kcal) jelly doughnu

Question

A 47-kg woman cheats on her diet and eats a 637-Calorie (637 kcal) jelly doughnut for breakfast.

(a) How many joules of energy are the equivalent of one jelly doughnut?
J

(b) How many stairs must the woman climb to perform an amount of mechanical work equivalent to the food energy in one jelly doughnut? Assume the height of a single stair is 15 cm.
stairs

(c) If the human body is only 21% efficient in converting chemical energy to mechanical energy, how many stairs must the woman climb to work off her breakfast?
stairs

Explanation / Answer

a) 637 Kcal = 637 x 1000 x 4.18 Joules = 2662660 Joules

b) Work done in climbing one stair = mgh = 47 x 9.8 x 0.15 = 69.09 Joules
therefore Stairs that should be climbed = 38539 Steps

c) Since human body is 21% efficient in converting chemical energy to mechanical energy therefore
Total energy that would be converted would be 21% of 2662660 Joules which is 559158.6 Joules

Number of stairs to be climbed now = 559158.6/69.09 = 8094 steps

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