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Angular displacement & velocity

  1. Jul 30, 2009 #1
    1. The problem statement, all variables and given/known data
    After fixing a flat tire on a bicycle you give the wheel a spin. Its initial angular speed was 7.05 rad/s and it rotated 13.7 revolutions before coming to rest. What was its average angular acceleration?



    2. Relevant equations
    ω2 = 2 alpha . theta


    3. The attempt at a solution
    ωi = 7.5 rad/s
    ωf = 0
    theta = 13.7 rev = 86.04 rad
    alpha = ?

    Using the above equation : alpha = -0.327rad/s^2. But the answer is wrong. Could someone help me??

    Thanks in advance
     
  2. jcsd
  3. Jul 30, 2009 #2
    EDIT: Ignore this post. The poster below is correct.
     
    Last edited: Jul 30, 2009
  4. Jul 30, 2009 #3

    kuruman

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    Angular acceleration is change in angular velocity divided by the time interval over which this change takes place. The dimensions don't come out right otherwise.

    Your numerical answer seems to be correct. what makes you think it is not?
     
  5. Jul 31, 2009 #4
    When I enter that answer in the box (masteringphysics HW), it says try again. So thought it might be a wrong answer.
     
  6. Jul 31, 2009 #5

    kuruman

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    In my opinion, "Mastering Physics" sometimes behaves incredibly stupidly and by this I mean it asks ambiguous questions. Try entering your answer without the negative sign.
     
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