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Homework Help: Angular acceleration?

  1. Oct 30, 2003 #1
    A rotating wheel requires 2.93 s to complete 37.0 revolutions. Its angular speed at the end of the 2.93 s interval is 97.1 rad/s. What is the constant angular acceleration of the wheel?

    I know this should be easy. I'm just missing something. I figured 37 rev = 232 rad (=theta). Then I used the kinematic
    Theta(f) = Theta(i)+(omega)(i)t+(1/2)(alpha)(t^2). But somehow it isn't working out. I know the answer should be around 15 or so but I keep getting 120 rad/sec^2!!
     
  2. jcsd
  3. Oct 30, 2003 #2

    jamesrc

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    You can't use your initial equation directly because you don't know the initial velocity yet. Use ωf = (ωi) + α*t; to find ωi. Then you can plug that in to your other constant acceleration question to find α. If I did it correctly, the acceleration should come out closer to 10 rad/s
     
  4. Oct 30, 2003 #3
    How can you use ùf = (ùi) + á*t to find ùi when you don't know what á is?

    (alright well you know what those symbols should mean)
     
  5. Oct 30, 2003 #4

    jamesrc

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    You solve for ωi in terms of α and plug it into the other equation. It's a system of 2 equations with 2 unknowns.
     
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