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Homework Help: Two blocks with pulley, friction

  1. Apr 10, 2010 #1
    1. The problem statement, all variables and given/known data
    Consider the setup shown below. The blocks
    have masses 8.2 kg and 25 kg. The pulley
    has mass 5.9 kg, and is a uniform disc with
    radius 0.25 m. Assume the pulley to be fric-
    tionless, but the coefficient of friction between
    the block and the surface is 0.28.What is the
    acceleration of the blocks? Assume the 25 kg
    mass is descending with acceleration a. The
    moment of inertia of the disk is 1/2MR2 and the
    acceleration of gravity is 9.8 m/s2 .
    Answer in units of m/s2.

    2. Relevant equations
    Torque= (radius)(force)sin(angle between them)= (inerta)*(alpha)or (inertia)*a/r
    friction= (mew)*(normal force)

    3. The attempt at a solution
    mo= mass of pulley

    I think this problem just has too much algebra =.=
    sumF1x= m1gsin(theta)+Friction-T1=m1a
    sumT= 1/2(mo)ra= rt1-rt2 ( I don't know which one should go first or why)
    solving the t and plugging it into torque I receive:

    a= g( (1+(mew))m1sin(theta)-m2)

    I have a practice problem I can use to verify if i set this problem up but I keep getting like .05 off -.-

    Any help would be appreciated!
    Last edited: Apr 10, 2010
  2. jcsd
  3. Apr 10, 2010 #2


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