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Homework Help: Moment of Inertia and Disk

  1. Nov 18, 2006 #1
    A uniform disk is attached at the rim to a vertical shaft and is used as a cam. The disc has a diameter of 38 cm. The moment of inertia of the disk about the axis of the shaft is 7.5*10^-3 kg*m/s. The shaft rotates uniformly about its axis at 70 rpm. The mass of the disc is closest to:

    a.0.12 kg
    b. 0.092 kg
    c. 0.14 kg
    d. 0.18
    e.0.16 kg

    I don’t know why the angular velocity is given. This is what I managed to do:

    Using parallel axis theorem,

    I_p = I_cm + M*d^2 = 0.5*M*r^2 + M*r^2 = 1.5*M*r^2

    M = (I_p)/(1.5*r^2) = (0.0075 kg*m/s)/(1.5*.19 cm^2) = 0.1385 kg

  2. jcsd
  3. Nov 19, 2006 #2
    Is this the right track?

    Thanks again.
  4. Nov 19, 2006 #3

    Doc Al

    User Avatar

    Staff: Mentor

    Looks good to me.
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