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-   -   Time needed to burn up calories (https://www.askmehelpdesk.com/showthread.php?t=288193)

  • Dec 4, 2008, 02:44 AM
    visharad
    Time needed to burn up calories
    This is not a homework question because I have completed my school/college. I am posting this question here because somebody asked me and it confuses me. So I want to know (as soon as I can) how to solve it.

    Each pound of fat contains 3500 food calories. When the body metabolizes food, 80.0 % of this energy goes to heat. Suppose you decide to run without stopping, an activity that produces 1290 W of metabolic power for a typical person.
    For how many hours must you run to burn up 1.00 lb of fat?

    Now, let me explain what confuses me in this question. I solved it as follows:-

    Total energy in 1 lb of fat = 3500 food calories = 3500 * 1000 cal = 3500 * 1000 * 4.18 J = 1.463 * 10^7 J
    Metabolic energy E = 20% of 1.463 * 10^7 J = 1.463 * 10^7 * 20/100 = 2.926 * 10^6 J
    Metabolic power P = 1290 W
    Time t = E/P = 2.926 * 10^6/1290 = 2268.217 sec = 2268.217/3600 hour = 0.63 hour
    Ans: 0.63 hour

    But this answer is wrong. I thought that 80% is lost into heat. So 20% should be metabolic energy. But that seems to be wrong.
    So let me know what I am doing wrong.
  • Dec 4, 2008, 07:23 AM
    ebaines

    Where did you get the figure of 1290 watts of "metabolic power" for a typical person? That sounds like a lot, especially if this person has to produce this much power continuously during exercise. Given your figure of 20% efficiency of the person's muscles, this means the person is producing heat at a rate of 1290*4 = 5160 watts! I sincerely doubt that this is possible.
  • Dec 4, 2008, 11:57 AM
    Capuchin

    Given the numbers you state, the math looks right, but I would check that power figure.

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