A 62-kg woman cheats on her diet and eats a 730-Calorie (730 kcal) jelly doughnu

Question

A 62-kg woman cheats on her diet and eats a 730-Calorie (730 kcal) jelly doughnut for breakfast.

(a) How many joules of energy are the equivalent of one jelly doughnut?
(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.
(c) If the human body is only 27% efficient in converting chemical energy to mechanical energy, how many stairs must the woman climb to work off her breakfast?

Explanation / Answer

Part a

As 1 kcal = 4184 joul so

730 kcal = 4184x730 = 3054320 J

Part B

As height of single stair, h= 15 cm = 0.15 m

Mass of woman, m = 62 kg

Hence work done = nmgh = 3054320

n = 3054320/62*9.8*0.15 = 33512.398 = 33512

Part c

As per given condition

nmgh = (27/100)*3054320

n = {(0.27)*3054320}/62*9.8*0.15 = 9048.348

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