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Homework Help: Fun Power Question

  1. Nov 10, 2013 #1
    1. The problem statement, all variables and given/known data
    Found a pretty fun question on power from one of my friends old physics exams just wanted to see if I was doing it right so far.

    3. The attempt at a solution
    So the first thing I did was draw a free body diagram and used Newtons Second law so

    ƩFx: F - (250 + 0.7v^2) - mgsin10 = ma

    Says that the driving force F must overcome the frictional force, so then ma = 0 and F = 250 + 0.7v^2 + mgsin10. A little stumped here, I am trying to find out the velocity, but I have two unknowns and one equation (please don't give me the answer, I want to solve it myself)!
    Last edited: Nov 11, 2013
  2. jcsd
  3. Nov 10, 2013 #2


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    Hi Panphobia! :smile:

    (try using the X2 and X2 buttons just above the Reply box :wink:)
    I'm confused … the question says a = 1 and v = 27. :confused:
  4. Nov 10, 2013 #3
    But that is initial, the v is always changing, and in my head I was thinking that there is a maximum velocity because of the air resistance. Oh my was I overthinking that? But anyway I was actually talking about deriving an expression for the power P that is required to drive the wheels. The other part is pretty easy.
    Last edited: Nov 10, 2013
  5. Nov 10, 2013 #4
    Then F = 1150 + 250 + 0.7(27)^2 + (1150)(9.8)sin10
    P = Fv
    P = 3867.3*27
    = 104 kW or 140 hp

    Deriving would just be without numbers right?
  6. Nov 10, 2013 #5


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    (i haven't checked your calculations, but …)

    yes, those equations look correct :smile:
    an expression would be without numbers, yes :wink:
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