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Homework Help: Mass of cylinder

  1. Dec 17, 2012 #1
    1. The problem statement, all variables and given/known data

    A light string is wrapped around a solid cylinder and a 300 g mass hangs from the free end of the string, as shown. When released, the mass falls a distance 54 cm in 3.0 s. Calculate the mass of the cylinder?

    2. Relevant equations

    not sure

    3. The attempt at a solution

    I have gotten as far as to determine the Tension on the string of -2.9N. Without known the radius of the cylinder I feel that the mass cannot be determined.

    Granted these are study question but if the final is going to be like this...yikes :surprised
  2. jcsd
  3. Dec 17, 2012 #2


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    hi doub! :smile:
    the motion depends on what i call the rolling mass of the cylinder, I/r2, which is always half the actual mass! :wink:

    carry on … you should find that the radius cancels out :smile:
  4. Dec 17, 2012 #3
    The best I can get is

    [itex]\alpha[/itex] = (T1 + T2)/I

    = (Fr - Tr)/1/2 mr2

    = (mra -(ma+mg)r)/ 1/2 mr2

    don't see how the radiii cancel each other though
  5. Dec 17, 2012 #4


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    sorry, i don't understand any of this :redface:

    you should have an F = ma equation and a τ = Iα equation
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