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Homework Help: Evaporation of perspiration

  1. Nov 28, 2006 #1
    When you jog, most of the food energy you burn above your basal metabolic rate (BMR) ends up as internal energy that would raise your body temperature if it were not eliminated. The evaporation of perspiration is the primary mechanism for eliminating this energy. Determine the amount of water you lose to evaporation when running for 30 minutes at a rate that uses 400 kcal/h above your BMR. (That amount is often considered to by the "maximum fat-burning" energy output.) The metabolism of 1 gram of fat generates approximately 9.2 kcal of energy and produces approximately 1 gram of water. (The hydrogen atoms in the fat molecule are transferred to oxygen to form water.) What fraction of your need for water will be provided by fat metabolism?

    Well, I found that the latent heat of vaporization of water is 2.5 x 10^6 J/kg
    and that I need to use the formula Q=mL but I don't know where to start.
  2. jcsd
  3. Nov 28, 2006 #2


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    Well, how much total energy do you burn doing the exercise? How much fat is required to produce the energy?

    Can you supply the final two steps...

    BTW, you'll need the latent heat of vaporization expressed in calories rather than joules.
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