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Homework Help: Power - biking uphill

  1. Oct 16, 2008 #1
    1. The problem statement, all variables and given/known data
    A bicyclist coasts down a 6.0 degree hill at a steady speed of 4.5 m/s.
    Assuming a total mass of 60 kg (bicycle plus rider), what must be the cyclist's power output to climb the same hill at the same speed?

    2. Relevant equations
    Newton's 1st law
    P=W/t

    3. The attempt at a solution
    [tex]P=\frac{W}{t}=F \cdot v[/tex]

    Set x-axis along incline...
    [tex]F-mg\sin\theta=0[/tex]
    [tex]F=mg\sin\theta[/tex]
    [tex]P=mg\sin\theta*4.5 = 276.6 W[/tex]

    To 2 sigfig = 280 W

    Is this correct? I'm being told it is the wrong answer...
     
  2. jcsd
  3. Oct 16, 2008 #2
    It looks right.
    Who told you that is not?
     
  4. Oct 16, 2008 #3
    The site where I submit my homework =/ I can't find any problem with it either, so I dunno whats up - guess I'll go ask the professor tomorrow. Thanks for checking my work and please let me know if you do think of somewhere I went wrong.
     
  5. Oct 17, 2008 #4
    Just an update... since the rider coasts down the hill but isn't accelerating, we must assume that there is a retardant force which must also be factored in when going uphill. This is where I went wrong. Kind of a trick question... blah!
     
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