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

1 calorie =4.18 J

=>637 kcalories =637*1000/4.18 =152.4k J or 152400 J

47*10*x =152400 J => x =152400/470 =324.25 m or 32425 cm

=> Number of steps =32425/15 = 2162 steps

21% effcient => 0.21*2162 steps = 454 steps

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