A 47 kg woman cheats on herdiet and eats a 470 Calorie(540 kcal) jelly donut for

Question

A 47 kg woman cheats on herdiet and eats a 470 Calorie(540 kcal) jelly donut for breakfast. (a) How many joules of energy are the equivalent of one jellydoughnut?
J

(b) How many stairs must the woman climb to perform an amount ofmechanical work equivalent to the food energy in one jellydoughnut? Assume the height of a single stair is 15 cm.
stairs

(c) If the human body is only 28% efficient in converting chemical energyto mechanical energy, how many stairs must the woman climb to workoff her breakfast?
stairs (a) How many joules of energy are the equivalent of one jellydoughnut?
J

(b) How many stairs must the woman climb to perform an amount ofmechanical work equivalent to the food energy in one jellydoughnut? Assume the height of a single stair is 15 cm.
stairs

(c) If the human body is only 28% efficient in converting chemical energyto mechanical energy, how many stairs must the woman climb to workoff her breakfast?
stairs

Explanation / Answer

For part (a), we just convert kcal to Joules using the conversionfactor 1 kcal = 4187 J. Then for (b), we find a height h such that m g h =(answer from part a) where m is the mass of the woman and g theacceleration due to gravity. Divide through by m g to get (answerfrom a)/m g = h. Finally, divide h by .15 m to get the number of 15cm steps For part c, we can multiply the answer in (b) by the woman'sefficiency to get the number of steps.

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