A 47 kg woman cheats on her diet andeats a 470 Calorie (540 kcal) jellydonut for

Question

A 47 kg woman cheats on her diet andeats a 470 Calorie (540 kcal) jellydonut for breakfast. (a) How many joules of energy are theequivalent of one jelly doughnut?
1 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.
2stairs

(c) If the human body is only 28%efficient in converting chemical energy to mechanical energy, howmany stairs must the woman climb to work off her breakfast?
3 stairs (a) How many joules of energy are theequivalent of one jelly doughnut?
1 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.
2stairs

(c) If the human body is only 28%efficient in converting chemical energy to mechanical energy, howmany stairs must the woman climb to work off her breakfast?
3 stairs

Explanation / Answer

mass of woman m = 47 kg energy taken by woman E = 540 kcal                                        = 540 * 10 ^ 3 * 4.186 J                                        = 2.26044 * 10 ^ 6 J (b). mechanical energy = food energy                      m g H = E from this height H = E / mg                             = 4907.59m height of single stair h = 15 cm = 0.15 m So, No.of stair N = H / h                            = 32717 (c). efficiency n = 28 % mechanical energy = 28 % of 2.26044 * 10 ^ 6 J                 mgH' = 632.9232* 10 ^ 3 J                     H ' = 632.92 * 10 ^ 3 / ( 47 * 9.8 )                          = 1374.12 No.of stairs N ' = H ' / h                         = 9160

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