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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

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

    Set x-axis along incline...
    [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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