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Homework Help: Solid disk accelerated

  1. May 5, 2009 #1
    1. The problem statement, all variables and given/known data
    A solid disk starts from rest and is accelerated to 25 rad/s in 12 sec. The mass of the disk is 4 kg and the radius is 0.15 m.

    What was the angular acceleration of the disk?

    What torque was needed to do this?

    How much work was done on the disk in this time?

    2. Relevant equations

    I = ½*M*R^2
    W= torque*theta

    3. The attempt at a solution
    Angular accel => Omega = Omega_initial + at
    25 = 0 + a(12)

    not sure what to do for the torque or work parts
  2. jcsd
  3. May 5, 2009 #2


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    Homework Helper

    Torque is also equal to I * a where I = is the moment of inertia which you already have and the angular acceleration you also have just developed in a).

    And there you go. You have the formula for the work. Just do it.
  4. May 5, 2009 #3
    Using I * a, I get [.5*4*.15^2]*2.1 = .095 for torque.

    For work, if I plug that in -- .095*25, I don't get one of the multiple choice answers. [This problem set has multiple choice answers.]
  5. May 5, 2009 #4


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    Homework Helper

    W = T*θ

    not T*ω.

    This link might help you find θ.

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