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Homework Help: Angular acceleration with a mass

  1. Nov 23, 2013 #1
    1. The problem statement, all variables and given/known data

    1) A solid cylinder of mass M = 1.54 kg and radius r = 0.100 m pivots on a frictionless bearing. A string wrapped around the cylinder pulls downward with a force F that equals the weight of a 0.590 kg mass, i.e., F = 5.782 N. Calculate the angular acceleration of the cylinder.

    2)If instead of applying the force F, a mass m = 0.590 kg is hung from the string, what is the angular acceleration of the cylinder?

    2. Relevant equations

    3. The attempt at a solution

    I found the answer to 1) to be 75.1 rad/s^2.

    For 2) I have been doing this:

    m*g*r = T

    angaccel = t/l

    Inertia moment for a solid cylinder = 1/2mr^2

    angaccel = t / 1/2mr^2

    using my numbers that gives me:

    (.5782)/(.5*1.54*.1^2) = 75.091 rad/s^2

    This is wrong. I have tried 8 times now on the same question and cannot get it, any help?
  2. jcsd
  3. Nov 23, 2013 #2


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    Science Advisor
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    Gold Member

    Hint: Since the 0.590Kg mass is accelerating downwards the tension it generates isn't mg.
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