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Find MASS of a runner when work, power, and velocity are given?

  1. Oct 25, 2009 #1
    1. The problem statement, all variables and given/known data
    While running in a cross country meet, a member of the team dissipates about 0.35J of mechanical energy per step per kg of her body mass. If she develops a power of 75W during the race and runs at a speed of 5m/s, find her mass.
    PS: Consider one [of her] running steps to be 1m.


    2. Relevant equations
    I am unsure what equation to use to find mass. I know the equations to find power and work, but in relation to finding mass I am unsure.


    3. The attempt at a solution
    I cannot attempt a solution with no clue what equation to use to get me started.
    I am able to do the work if I have proper equations.
    Thanks!
     
  2. jcsd
  3. Oct 25, 2009 #2

    Delphi51

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    Homework Helper

    Looks like the 75 Watts goes into making those steps.
    P = W/t so you need to figure out the work done stepping over some convenient time. Maybe you could do it for one step?
     
  4. Oct 25, 2009 #3
    I am not sure what equation is used to find the mass though?
     
  5. Oct 25, 2009 #4

    Delphi51

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    It says the energy used is 0.35 J per kg. So the energy used is 0.35*m.
    If you put that in the equation, you'll be able to solve for m.
     
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