How Many Food Calories with Efficiency %

In summary, when comparing the efficiency of an out of condition professor and a well-conditioned athlete, the professor has an efficiency of 10% while the athlete has an efficiency of 25%. This means that the athlete would metabolize 201 food calories while doing the same amount of work as the professor, who metabolizes 500 food calories.
  • #1
6
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I figured out (a) but I am having trouble with (b):
(a) What is the efficiency of an out of condition professor who 2.10e5 J of useful work while metabolizing 500 kcal of food energy?
(b) How many food calories would a well-conditioned athlete metabolize in doing the same work with an efficiency of 25%?

Homework Equations


OE + Wnc = OEf
η = Work_out / Work_in
Work_in = η * work_out

The Attempt at a Solution


For (a) I converted the calories to Joules
1 kcal = 4184 J
500 kcal (4184J/1 kcal) = 2.1e6 J

η = W_out/W_in
η = (2.10e5J) / (2.10e6J)
η = 10%

(b) I assume I could input the 25% into the equation and work backwards but it's not giving me a correct anwser. I've tried the following:

0.25 = (2.10e5J) / (kcal)
kcal = (0.25)(2.10e5J)
kcal = 52500J
Convert the Joules to kcal and get something like 12kcal

But that's wrong also.
 
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  • #2
I realize that I wrote my equation wrong at the end I said that it should be η*work_out but it is work_out/η . Here is how I finalized the problem:

η = work_out / work_in

0.25 = (2.10e5) / (kcal)

kcal = (2.10e5) / (0.25)

kcal = 840e3 J

J to kcal 1kcal = 4184 J

840e3 / 4184 = 201 kcal
 

1. How are food calories measured?

Food calories are measured using a device called a bomb calorimeter, which burns a small sample of the food and measures the amount of heat produced. The heat is then converted into calories using the first law of thermodynamics.

2. What is the difference between calories and food calories?

Calories refer to the amount of energy needed to raise the temperature of 1 gram of water by 1 degree Celsius. Food calories, on the other hand, refer to the amount of energy in food that the body can use for fuel. One food calorie is equal to 1,000 regular calories.

3. How is the efficiency of food calories calculated?

The efficiency of food calories is calculated by dividing the number of calories that the body can actually use from a food by the total number of food calories. This percentage is then multiplied by 100 to get the efficiency percentage.

4. Does the efficiency of food calories vary from person to person?

Yes, the efficiency of food calories can vary from person to person based on factors such as age, gender, body composition, and activity level. Generally, people with more muscle mass and higher activity levels have a higher efficiency of food calories.

5. Can the efficiency of food calories be increased?

Yes, the efficiency of food calories can be increased through regular exercise and building muscle mass. Eating a balanced diet with a variety of nutrient-dense foods can also improve the body's ability to use food calories efficiently.

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