A 51 kg woman cheats on herdiet and eats a 433 Calorie(540 kcal) jelly donut for

Question

A 51 kg woman cheats on herdiet and eats a 433 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 30% 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 30% efficient in converting chemical energyto mechanical energy, how many stairs must the woman climb to workoff her breakfast?
stairs

Explanation / Answer

mass of woman m = 51 kg energy E = 433 kcal (a). In joules E = 433 * 10 ^ 3 * 4.168 J                        = 1804.744 * 10 ^ 3 J    Since 1 cal = 4.186J (b). Mechanical energy = food energy                       m g h = 1804.744 * 10 ^ 3 J from this height h = ( 1804.744 * 10 ^ 3 J ) / ( 51 kg *9.8 m / s ^ 2 )                           = 3610.9323 m So, No.of stairs n = h / 15 cm = 24072 stairs (c). mechanical energy = 30 % of chemical energy                               E' = 0.3 E So, No.of stairs N = E ' / m g                             = 7221

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