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Homework Help: Power of a man cycling up a hill.

  1. Jun 24, 2011 #1
    1. The problem statement, all variables and given/known data

    What power must a man of mass 85 kg have to bicycle 850m up a hill, inclined at 5.2 degrees to the horizontal, at a constant speed of 15.6 m/s? The force of friction on the man and the bicycle is 175N parallel to the incline.

    m = 85 kg

    d = 850m

    dy = 850m * sin5.2

    v = 15.6 m/s

    Ff = 175N


    2. Relevant equations

    P = W/t

    t = d/v

    Wnet = Fnetd = KE

    KE1 + PE1 = KE2 + PE2


    3. The attempt at a solution

    Old solution:

    New Solution:

    Wnet = KE2-KE1

    KE1 + PE1 = KE2 + PE2 + Eh

    Wnet = - PE2 - Eh

    P = (-PE2 - Eh)/(d/v)

    P = (-85*9.8*850sin5.2 - (-175*850))/(850/15.6) = 1600 W
     
    Last edited: Jun 24, 2011
  2. jcsd
  3. Jun 24, 2011 #2

    ehild

    User Avatar
    Homework Helper

    As power=F*v (force times velocity) your second solution is correct.

    ehild
     
  4. Jun 24, 2011 #3
    Thank you, I didn't know that.
     
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