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## Sara, who weighs 66 kg, is on a guilt trip after eating a 788-Calorie (788 kcal) breakfast of pancakes loaded with fruits, cream, and syrup.

Question

Sara, who weighs 66 kg, is on a guilt trip after eating a 788-Calorie (788 kcal) breakfast of pancakes loaded with fruits, cream, and syrup. She decides to work out before going to her weekly weight-watchers’ meeting. If the height of a single stair is 12 cm, and her body is only 25% efficient in converting chemical energy to mechanical energy, determine the number of stairs Sara must climb to cancel out the Calories consumed.

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Physics
5 months
2021-08-23T10:25:24+00:00
2021-08-23T10:25:24+00:00 1 Answers
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## Answers ( )

Answer:Sara must climb 10609 stairs to burn this food.Explanation:Chemical energy content in Sara’s body = 788 kCal x 4.184 = 3296.99 kJ = 3296990 J

her body is only 25% effective in converting chemical to mechanical energy, therefore,

available mechanical energy = 25% of 3296990 = 0.25 x 3296990 =

824247.5 J –this is equivalent to the work she must do to burn this stored energyflight of stairs = 12 cm = 0.12 m

Sara’s mass m = 66 kg

Sara’s weight = mg = mass x acceleration due to gravity 9.81 m/s^2

weight W = 66 x 9.81 = 647.46 N

work done = force x distance climbed d

putting in the necessary values, we have

824247.5 = 647.46 x d

d = 1273.05 m

the number of stairs Sara must climb is equal to the distance climbed divided by the height of a single stairs

number of stairs = 1273.05/0.12 = 10608.75 ≅

10609 stairs