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Homework Help: Mass of pulley

  1. Mar 8, 2010 #1
    1. The problem statement, all variables and given/known data
    The two masses(m1 = 5.0 kg and m2 = 3.0 kg) in the Atwood's machine shown below are released from rest, with m1 at a height of 0.75 m above the floor. When m1 hits the ground its speed is 1.8 m/s. Assuming that the pulley is a uniform disk with a radius of 12 cm, determine the pulley's mass.

    http://img23.imageshack.us/img23/904/pulleyl.jpg [Broken]​
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    2. Relevant equations
    Rotational kinematics


    3. The attempt at a solution
    I don't really know where to start here. Could someone please start me off?
     
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Mar 8, 2010 #2

    rl.bhat

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    Initial and final velocity of m1 is given. h is given. Find acceleration of m1. m2 and pulley will have the same acceleration. Write down the expression for a to them. Then solve for the mass of the pulley.
     
  4. Mar 8, 2010 #3
    Is the final velocity of m2 also 1.8 m/s? And is the mass of the pulley simply the mass of the disk?
     
  5. Mar 8, 2010 #4

    rl.bhat

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    Yes.
     
  6. Mar 8, 2010 #5
    So I found the acceleration to be 2.16 m/s^2.

    Now is the acceleration of the pulley 2.16/0.12 = 18 rad/s^2?

    So how do I find the mass?
     
  7. Mar 8, 2010 #6
    Alright! You are almost there. You can say that net torque on the disk is [tex]\tau=I\alpha[/tex]
     
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