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Homework Help: Angular rotation

  1. May 2, 2005 #1
    I've been trying to do this question in the text book, but I can't seem to get the answer.

    Emilie's potter's whel rotates with a constant 2.25 rad/s^2 angular acceleration. After 4 seconds the wheel has rotated through an angle of 60.0 rad. What was hte angular velocty of the wheel at the beginning of the 4.00 second interval.

    I thought I could use a = (w2-w1)/ (t2-t1), but I end up with 6 as my answer, which is incorrect.

    Thank you in advance.
     
  2. jcsd
  3. May 2, 2005 #2

    SpaceTiger

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    Perhaps this thread will help.
     
  4. May 2, 2005 #3
    Ok, ive got it. But why is my method incorrect?
     
  5. May 2, 2005 #4

    SpaceTiger

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    Because:

    [tex]\omega_2\ne\frac{\Delta \theta}{\Delta t}=15\ rad/s[/tex]

    Actually,

    [tex]\bar{\omega}=\frac{\omega_2+\omega_1}{2}=\frac{\Delta \theta}{\Delta t}[/tex]
     
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