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Torque in circular motion

  1. Nov 8, 2009 #1
    1. The problem statement, all variables and given/known data
    When play is pressed, a cd accelerates uniformly from rest to 500 rev/min in 3.0 revolutions. If the Cd has a radius of 5.5 cm, and a mass of 20 g, what is the torque?


    2. Relevant equations
    not sure, this is my problem. i think its torque=angular acceleration*inertia. but i dont know how to turn "500 rpm in 3.0 revolutions" into angular acceleeration


    3. The attempt at a solution
    nothing, i dont how to make the equations work
     
  2. jcsd
  3. Nov 8, 2009 #2
    You have your analogy from linear kinematics equations to rotational motion equations.

    a = delta v / delta t

    So the same is true for rotational acceleration, and change in rotational velocity
     
  4. Nov 8, 2009 #3
    but how does torque fit into this equation?
     
  5. Nov 9, 2009 #4
    You can use: [tex]\omega^{2}=2\alpha s[/tex] , where [tex]s=2\pi r * 3[/tex] (3 times the circumference)

    and 500 [tex]rev/min=4770 rad/sec[/tex]
     
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