A 53 kg person eats a 518 Calorie (518 kcal) jelly doughnut for breakfast. (a) H

Question

A 53 kg person eats a 518 Calorie (518 kcal) jelly doughnut for breakfast.

(a) How many joules of energy are the equivalent of this jelly doughnut?

(b) How many steps must this person climb on a very tall stairway to change the gravitational potential energy of the person-Earth system by a value equivalent to the food energy in one jelly doughnut? Assume the height of a single stair is h = 15 cm.

(c) If the human body is only 22% ecient in converting chemical potential energy to mechanical energy, how many steps must the person climb to work off this delicious, amazing breakfast, and how tall of a staircase does this correspond to?

Explanation / Answer

a) in joules = 518*1000*4.2J = 2175.6kJ

b) let the heght be h metres then

mgh=2175.6*1000

=>h=2175.6*1000/53*9.8=4188m

so steps = 4188*100/15=27925 steps

c) if the efficiency will be 22% then energy needed to spent=0.22*2175*6*1000=478632J

hence hieght=478632/53*9.8=921.50m=92150cm

hence steps=92150/15=6143 steps

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