A 62 kg woman cheats on her diet and eats a 637 Calorie (637 kcal) jelly donut f

Question

A 62 kg woman cheats on her diet and eats a 637 Calorie (637 kcal) jelly donut 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 28% efficient in converting chemical energy to mechanical energy, how many stairs must the woman climb to work off her breakfast?
stairs

Explanation / Answer

a) 637,000 * 4.184J/cal = 2.7*106 J

b) mgh = E

h = E/mg = 2.7*106 / (62*9.8) = 4386m

h/0.15m per step = 29,000 steps to 2 sig figs

c) multiply previous by 0.28 = 8200 steps to 2 sig figs.

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