A 55 kg woman cheats on her diet and eats a 602 Calorie (602 kcal) jelly donut f

Question

A 55 kg woman cheats on her diet and eats a 602 Calorie (602 kcal) jelly donut 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 25% efficient in converting chemical energy to mechanical energy, how many stairs must the woman climb to work off her breakfast?

Explanation / Answer

(A) 602 kCal = 602*4.18 kJ = 2516.36*103 J

= 2.52 MJ

(B) Let no. of stairs = n

height of one stair = 15 cm = 0.15 m

mgh = 2516.26*103

=> 55*9.8*n*0.15 = 2516.36*103

=> n = 31123.81 31124 stairs

(C) Total energy utilised = 25*2516.36*103/100 = 629090 J

=> 55*9.8*n*0.15 = 629090

=> n = 7780.95 7781 stairs

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