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Question by discostick12345: Do you think you can help? Please!!?
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 135 food calories per bar.

A-) If a 70.0 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?

B-) If, as is typical, only 23.0% 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.)

Best answer:

Answer by electron1
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 135 food calories per bar.

1 Food calorie must equal 1 Kilo calorie, because 1 calorie = 4.180 joules.
A-) If a 70.0 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?

Work = Energy
Work = Force * distance

When you climb, force = weight
Weight = mass * gravity

Work = mass * gravity * distance

Work = 70 * 9.8* d
Energy = 135 food calories * 4180 J/ food calorie =564,300 J

Work = Energy
70 * 9.8* d = 564,300
d = 822.6 meters

B-) If, as is typical, only 23.0% 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.)

Energy = 0.23 * 564,300 = 129,789

Work = Energy
70 * 9.8* d = 129,789
d = 189.2 meters

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