A 58-kg woman cheats on her diet and eats a 449-Calorie (540 kcal) jelly doughnu

Question

A 58-kg woman cheats on her diet and eats a 449-Calorie (540 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 29% efficient in converting chemical energy to mechanical energy, how many stairs must the woman climb to work off her breakfast?
stairs

Explanation / Answer

a. Energy = 451 x 4.184 = 1886.984 Joules b. E = n x mgh 1886.984 = n x 54 x 9.8 x 0.15 number = n = 23.77 stairs c. n = 23.77/0.23 = 103.354 stairs

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