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Homework Help: Atwood Machine with Friction

  1. Dec 14, 2009 #1
    1. The problem statement, all variables and given/known data
    Two masses are suspended from a pulley of mass m supported by an axle (Atwood machine).
    What is the net torque acting on the pulley wheel in terms of T1 and T2?

    There is friction between pulley and rope.
    Ropes are massless and pulley can rotate without friction about its own wheel.

    2. Relevant equations
    τ = I*α


    3. The attempt at a solution
    This is what I got so far:
    http://img685.imageshack.us/img685/4333/24667502.th.png [Broken]

    Others get τnet = (T1-T2)r
    Why??

    Thanks in advance!!
     
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Dec 14, 2009 #2
    Wait nevermind, I just realized that both tensions should be pointing downward.

    So, (T1-T2)=r is correct.

    Thanks anyways!!
     
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