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Homework Help: Find tension between blocks 2 & 3

  1. Feb 29, 2012 #1
    1. The problem statement, all variables and given/known data

    There are three blocks connected by strings as shown in the figure. Each block has the mass as following mass,
    Assuming there is no friction,

    2. Relevant equations


    3. The attempt at a solution

    In my FBD of the hanging box
    [itex]\uparrow[/itex] <--- Tension
    [itex]\downarrow[/itex] <--- W=mg

    ^^ in y direction: T-W=0

    The FBD of the box on the table
    [itex]\uparrow[/itex] <---Normal Force
    [] [itex]\rightarrow[/itex] <--- Tension
    [itex]\downarrow[/itex] <--- W=mg

    ^^ x direction: t=0
    y direction: Fn-W=O

    But im completely confused on how to find the tension of the boxes

    Attached Files:

  2. jcsd
  3. Feb 29, 2012 #2


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    Homework Helper

    Welcome to PF!

    Hi Rey4312! Welcome to PF! :smile:

    Call the tensions "T1" and "T2", and the acceleration "a" (it'll be the same for all three boxes, won't it? :wink:)

    Then do F = ma three times, once for each box, and solve …

    what do you get? :smile:
  4. Feb 29, 2012 #3
    But if i do that the acceleration = 0 and so it makes all the forces 0... right??

    or am i missing something and it should be gravity?
  5. Feb 29, 2012 #4


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    Homework Helper

    Yes, you need to include W (=mg) for the hanging box.
  6. Feb 29, 2012 #5
    W for the hanging box is 16.66

    and W for box 2(m2) is 21.56....

    Where do i go from there, because that doesn't give me acceleration....
  7. Feb 29, 2012 #6
    i figured it out... i ended up having to do m2a+m1a
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