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Homework Help: Finding angular acceleration for this prob

  1. Nov 19, 2004 #1
    A rotating wheel requires 3.00s to rotate 37.0 revolutions. Its angular velocity at the end of the 3.00-s interval is 98.0rad/s. What is the constant angular acceleration of the wheel?

    What i did was i used average w=delta(theta)/delta time. Then i used average w=radical(w^2+wo^2) to find wo. Then i plugged it all into w=wo+alpha(t) and i got alpha=12.67. The answer is suppose to be 13.7rad/s^2. Can someone help me on this problem?
    thanks
     
  2. jcsd
  3. Nov 19, 2004 #2
    There is a single formula, incorporating all the elements you are given: wf, t, theta, alpha. Find that, and just sub in values.
     
  4. Nov 20, 2004 #3
    What is the formula? The ones I have all have "wi" in it and I'm not sure I calculated that correctly.
     
  5. Nov 20, 2004 #4
    Here's how you calculate the initial angular velocity.

    Since angular acceleration is constant:
    [tex]\frac{\Delta\theta}{\Delta t}=\omega_{av}=\frac{\omega+\omega_{0}}{2}[/tex]
    Since one revolution is [itex]2\pi[/itex] radians,
    [tex]2\times\frac{37\times 2\pi}{3 s}-98.0\frac{rad}{s}=\omega_{0}[/tex]

    Now use [tex]\omega=\omega_{0}+\alpha\Delta t[/tex]
     
  6. Nov 20, 2004 #5
    That method works, as does using: theta = (wf)t - .5*alpha*t^2.
     
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