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Homework Help: A strange pre-test problem

  1. Oct 21, 2004 #1
    Hi!

    I have a big problem with this simple question. I can manage all the other questions on the paper i got except this one, and it's even one of the easier in there. So please gimme suggestions of what formulas to use:

    A person is struggeling his way up a 8 degree hill with the velocity of 12km/h. Calculate the power use. The total mass of him and his bicycle is 75kg. Air resistance and friction is 5,0% of mg.

    I tried calculating it with both force laws and energy laws and i end up with the answer 120W (or something i cant remember) but the correct answer should be 0,46kW

    Please excuse my bad english, and thanks for the help!

    Simon
     
  2. jcsd
  3. Oct 21, 2004 #2

    Doc Al

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    Staff: Mentor

    Welcome to PF!

    Show us how you got your answer and we'll give you a hand.
     
  4. Oct 21, 2004 #3
    Thanks!

    Unfortunately i've erased the first soultion and i've only got a lot of unreadable panic notes left :P but can u at least tell me what path to use, Energy or Force? Then i think i'll be able to solve it.

    Thanks in advance!
     
  5. Oct 21, 2004 #4

    Doc Al

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    Staff: Mentor

    Both methods should agree. Go ahead and use the "force" method. :smile:
     
  6. Oct 21, 2004 #5
    I think i'll manage it now, after hours of studying. Got a test tomorrow morning and i got a little scared that i couldn't accomplish a simple task like that. Btw i used the energy method but thanks for the advice :D

    take care and good night
     
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