A 49-kg woman cheats on her diet and eats a 608-Calorie (608 kcal) jelly doughnu

Question

A 49-kg woman cheats on her diet and eats a 608-Calorie (608 kcal) jelly doughnut for breakfast. (a) How many joules of energy are the equivalent of one jelly doughnut? J (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. stairs (c) If the human body is only 23% efficient in converting chemical energy to mechanical energy, how many stairs must the woman climb to work off her breakfast? stairs

Explanation / Answer

We know that 1 kcal = 4184 J mass = 58 kg a) 1 jelly implies 449 x 4184 J = 1878.616 kJ b) E = m g h h = E / m g = 1878616 / 58 x 9.8 = 3305.095m Therefore she can climb the stairs n = 3305.095 / 0.15 = 22033.97 c) h = 0.29 x 1878616 / 58 x 9.8 = 958.48m So number of stairs = 958.48/0.15 =6389.87

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