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Homework Help: Blocks and Pulleys Problem, please help!

  1. Oct 6, 2009 #1
    Three Blocks total, Two on sides hanging off the table, and one Block on table in the middle of the two outer blocks. . . symmetrical.

    block1 from left has a mass of M, hanging and connected to a pulley, which is the connected to Block 2(on a table) with Mass of 2M, Block three is also hanging but with mass of 2M. If acceleration is .5m/s^2, What is the Tension on the first string?
    what is the Kinetic friction of Black 2 on Table?


    I started by writing that Block 3= 2Mg-T2=2Ma
    Block 2= T2-T1=2Ma
    Block 1= T1-Mg=Ma
    I then connected Block3 to Block2, since they share T2
    I would add forces but tensions would simply cancel out, at times even masses and Tension, leaving me with known variables=known variables, makes not sense. I tried many ways. This is all the info the book gives, but I feel I'm missing a key idea.

    This has been driving me insane.
    The tension question was given to me on a test, which I failed answering correctly.
    The Kinetic question, I know from back of book, the coefficient of kinetic friction is = .37
    But I don't know how exactly how they got to it. Some one please help.
    1. The problem statement, all variables and given/known data

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. Oct 7, 2009 #2

    Doc Al

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    Staff: Mentor

    Don't forget that friction acts on Block 2.

    Correct your equation for Block 2 and you'll be able to solve for the friction, then use that to find μ.
  4. Oct 7, 2009 #3


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    Science Advisor
    Homework Helper

    Welcome to PF!

    Hi FabricWarp! Welcome to PF! :smile:

    (instead of using "SIZE" tags, try using the X2 and X2 tags just above the Reply box :wink:)
    ooh, you're missing the obvious … you need a 2µMg somewhere in there, don't you? :smile:
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