Answered

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The food calorie, equal to 4186 J, is a measure of how much energy is released when food is metabolized by the body. A certain brand of fruit-and-cereal bar contains 160 food calories per bar.
Part A
If a 67.0 kg hiker eats one of these bars, how high a mountain must he climb to "work off" the calories, assuming that all the food energy goes only into increasing gravitational potential energy?
Express your answer in meters.
Part B
If, as is typical, only 20.0 % of the food calories go into mechanical energy, what would be the answer to Part A? (Note: In this and all other problems, we are assuming that 100% of the food calories that are eaten are absorbed and used by the body. This is actually not true. A person's "metabolic efficiency" is the percentage of calories eaten that are actually used; the rest are eliminated by the body. Metabolic efficiency varies considerably from person to person.)
Express your answer in meters.

Sagot :

keijosalonen

Answer: 1 cal is 4.186 J, 1 kcal = 4186 J   A : 1014 m , B  200 m

Explanation:   A) Work done by climber is change in potential energy.

W = ΔEp = mgh = 67.0 kg· 9.81 m/s²· h = 160 kcal · 4186 J / kcal.

Solve h  =  160 kcal · 4186 J / kcal /67.0 kg· 9.81 m/s² = 1014 m

B  Energy is only 20 %  :   Then  h  =  0.20 ·160 kcal · 4186 J / kcal /67.0 kg· 9.81 m/s² = 200 m.

Actually, muscles also produce heat from most of the energy provided by food.

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