A 57-kg woman cheats on her diet and eats a 547-Calorie (547 kcal) jelly doughnu

Question

A 57-kg woman cheats on her diet and eats a 547-Calorie (547 kcal) jelly doughnut for breakfast.
(a) How many joules of energy are the equivalent of one jelly doughnut?

answer= 2289742 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.

Answer= 27327.15 stairs


(c) If the human body is only 30% efficient in converting chemical energy to mechanical energy, how many stairs must the woman climb to work off her breakfast?

answer= 8198.15 stairs


I understand the first 2 parts. Can anyone help explain in order to get the 3rd answer why you multiply the 30% by the 27327.15 stairs (answer B)?

Explanation / Answer

a) 547000*4.18 = 2286460 J b) 57*9.8*n*.15 = 2286460 n = 27288 c) 57*9.8*n*.15 = 2286460*.3 n = .3*27288 = 8186 it differs from ur answer bcz i take g as accurate 9.8 m/sec^2

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