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Homework Help: Burning calories

  1. Dec 3, 2008 #1
    1. The problem statement, all variables and given/known data

    If a person radiates about 67 W of power at room temperature, how long does it take (h) for a person to radiate away the energy acquired by consuming a 285 Calorie donut?

    2. Relevant equations
    i know W=J/s
    no clue, i need one that involves time.

    3. The attempt at a solution
    i've tried 285/67=4.25 sec...but thats wrong...
    and i don't think the problem is asking in Kcals
  2. jcsd
  3. Dec 3, 2008 #2


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    You need to figure out how many joules there are in 285 calories. And I'll bet they are talking about Kcal's. They almost always are when referring to food.
  4. Dec 3, 2008 #3
    285 Cal=285,000 cal (4.186)= 1.19e6 J

    how do i relate it to time though?
    do i just divide it by the power?
    1.19e6/67=17806 s/60/60=4.95 h
    ok thanks
  5. Dec 3, 2008 #4


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    Sure. J/(J/sec)=sec.
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