The food calorie, equal to 4186 J, is a measure of how much energy is released w

Question

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 140 food calories per bar.

1.) If a 73.0 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?

h = ?? m

2.) If, as a typical, only 25.0 % 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.)

h = ?? m

I have no idea how to do these problems. Please show step by step with correct answers so I can try to understand.

THANK YOU!!

Explanation / Answer

1. Gravitational PE = mass x gravity x height

The energy would be 4186 x 140 = 586,040 J

586,040 = 73(9.8) h

h = 819.17 m

2. h = 819.17(25%/100) = 204.79 m

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