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Two blocks and a pulley (please help, im confused)

  1. Mar 26, 2007 #1
    1. The problem statement, all variables and given/known data
    A block of mass m1 = 2 kg rests on a table with which it has a coefficient of friction µ = 0.56. A string attached to the block passes over a pulley to a block of mass m3 = 4 kg. The pulley is a uniform disk of mass m2 = 0.6 kg and radius 15 cm. As the mass m3 falls, the string does not slip on the pulley. With what acceleration does the mass m3 fall?

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. Mar 26, 2007 #2
    For a problem like this its always helpful to draw a free body diagram.

    You have a weight force acting on m3 equal to (m3)g, and a tension in the rope -T.


    On m2, you have a force of friction -uFn and the same tension force T, such that -uFn+T=(m2)a(net)

    If you add the two together, you will have a net tangential force (Ftan)acting on the pulley. And you know that t=RFtang=I*alpha=R(m3*g-um2g), and you have hte numbers to find I for the pulley, so you can find alpha which is a/r where a is the linear acceleration.

    I'm pretty sure I did that right.
  4. Mar 27, 2007 #3
    thanks a lot, that helped. i figured it out.
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