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How high can it coast up the hill, if you neglect friction?

  1. Jun 2, 2016 #1
    1. The problem statement, all variables and given/known data
    Suppose a 180 kg motorcycle is heading toward a hill at a speed of 29 m/s. The two wheels weigh 12 kg each and are each annular rings with an inner radius of 0.280 m and an outer radius of 0.330 m.
    How high can it coast up the hill, if you neglect friction in m?

    *m = 180 kg
    *v = 29 m/s
    *h = 32 m

    2. Relevant equations

    mgh = 1/2 m v^2 + 1/2 I w^2

    3. The attempt at a solution
    First thing I did is finding the moment of inertia for the wheels, which is 1/2 m (b^2 + a^2) then I multiplied it by 2 since there are two wheels.

    I then plugged that number for "I" in the above equation. I found w by dividing the given velocity by the outer radius(not sure if that is right) and then I had all the variables and solved for h but got an unreasonable number! bigger that the actual height of the hill.
     
  2. jcsd
  3. Jun 3, 2016 #2

    haruspex

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    It's hard to be sure without seeing all your working, but it sounds like you only considered the wheels getting up the hill. Even then, I don't think you should have got an unreasonable answer. If you do not show you working we cannot tell where you went wrong.
     
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