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Angular Acceleration of a Moving Wheel

  1. Feb 14, 2007 #1
    I am having a bit of trouble with the following problem.

    A cyclist starts from rest and pedals so that the wheels make 8.5 revolutions in the first 4.6 s. What is the angular acceleration of the wheels (assumed constant)?

    I multiplied 8.5 by 2pi and then divided by 4.6 sec. I get an answer of 11.6 rad/sec, but they want an answer in rad/sec^2. Am I doing this right?
     
  2. jcsd
  3. Feb 14, 2007 #2

    Hootenanny

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    I see you've found the Homework Forums, :wink:.

    Not quite. What is the definition of angular acceleration?
     
    Last edited: Feb 14, 2007
  4. Feb 14, 2007 #3
    Angular Acceleration

    The definition of angular acceleration is angular velocity over time. So, to get angular velocity from 8.5 rev/4.6 sec you have to find the angular velocity first. So, the definition of angular velocity (omega) is angular displacement over time, and the angular displacement is in radians. That is why I multiplied 8.5 by 2pi. Do I have to divide by 4.6 again?
     
  5. Feb 14, 2007 #4

    Hootenanny

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  6. Feb 14, 2007 #5
    I looked at that website and this is what makes sense to me:

    8.5 rev * 2pi = 53.41 radians
    53.41 rad / 4.6 sec = 11.61 rad/sec (omega)
    11.61 rad/sec / sec = 2.5 rad/sec^2

    2.5 is the wrong answer when I entered it. I am out of ideas.
     
  7. Feb 14, 2007 #6

    Hootenanny

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    Okay, how about this section of the website;

    [​IMG]

    Which equation do you suppose would be appropriate in this case?
     
  8. Feb 12, 2009 #7
    wait what happened to this? was there an answer discussed? Im so confused! i have a very similar problem and Im doing the same thing.

    I think the right equation is w^2= wi^2+2a(theta)

    but i used that assuming the initial angular velocity is 0 and its wrong
     
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