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The Overheated Jogger

  1. Nov 21, 2008 #1
    While jogging, a 70.0-{\rm kg} student generates thermal energy at a rate of 1200 {\rm W}. To maintain a constant body temperature of 37.0{\rm ^{\circ} C}, this energy must be removed by perspiration or other mechanisms. If these mechanisms failed and the heat could not flow out of the student's body, irreversible body damage could occur.

    Protein structures in the body are irreversibly damaged if body temperature rises to 44.0{\rm ^{\circ} C} or above. The specific heat of a typical human body is 3480\;{\rm J/(kg \cdot K)}, slightly less than that of water. (The difference is due to the presence of protein, fat, and minerals, which have lower specific heat capacities.)

    For how long a time t could a student jog before irreversible body damage occurs?
    Express your answer in minutes.

    Okay so I used Q=mc(Tf-Ti) = 1705200J
    Then I divded that with the power given in the problem to obtain to time in sec since I know power is J/s
    I got 1421 s then I converted it to min -> 23.68min -> I entered 24min as my answer.

    I don't understand where I did wrong, it says:

    "Not quite. Check through your calculations; you may have made a rounding error or used the wrong number of significant figures."
  2. jcsd
  3. Nov 21, 2008 #2


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    Well, considering every number except for the 1200 has 3 significant figures, my guess is that the 1200 is supposed to have 4 significant figures and the correct answer would have been 23.7 minutes
  4. Nov 21, 2008 #3
    You are right, thank you so much.

    Man, I hate sig fig.
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