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Homework Help: Rotational Motion

  1. Jun 11, 2008 #1
    1. The problem statement, all variables and given/known data
    A tire placed on a balancing machine in a service station starts from rest and turns through 4.9 revolutions in 1.0 s before reaching its final angular speed. Calculate its angular acceleration.

    I need my answer in

    2. Relevant equations
    1rev= 2n rad

    3. The attempt at a solution
    Converted rev/s to rad/s
    4.9rev/s * (2n rad/s)/ 1 rev= 30.7876 rad/s

    a= (30.7876 rad/s)/ 1sec => 30.7876 rad/s^2

    This answer comes out wrong.

    What am I doing wrong?
  2. jcsd
  3. Jun 11, 2008 #2


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    Science Advisor
    Homework Helper

    It's not a constant angular velocity question. Angular velocity changes with time, so you can't just use a=w/t. You need a formula analogous to s=(1/2)*a*t^2 for linear motion. It looks very similar, just the meaning of the letters changes.
  4. Jun 11, 2008 #3
    Okay thanks. I get it now.
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