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Homework Help: Some help needed

  1. Nov 3, 2004 #1
    While running, a person dissipates about 0.554 J of mechanical energy per step per kilogram of body mass. If a 62.5 kg runner dissipates a power of 65.4 W during a race, how fast is the person running? Assume a running step is 1.50 m in length.

    Well I know that the person loses 34.6 J of mech energy every 1.5 m and loses a total of 65.4 watts during the entire race. Now 65.4 W is just 65.4 J/s, so how can I further relate all of these givens? I am a little confused. Thanks for any help in advance.
  2. jcsd
  3. Nov 3, 2004 #2
    In one step, the amount of energy dissipated is given by

    [tex](62.5kg)(0.554Jkg^{-1})[/tex] (per step or per 1.50m)

    Suppose there are n steps. This corresponds to a distance 1.50n meters. Hence in n steps the energy dissipated per unit time is

    [tex](62.5)(0.554)(n) = 65.4[/tex]

    from this you can get the number of steps he covers in unit time. Multiply it by 1.50m to get the speed. Is this okay?

  4. Nov 3, 2004 #3
    Thanks for the help.
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