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Tension Force (should be easy)

  1. May 10, 2012 #1
    1. The problem statement, all variables and given/known data

    The weights of the blocks are W_A = 120 lb and W_B = 20 lb, and the surfaces are smooth. Find the acceleration of block A.

    [A picture is shown. Block A is connected via rod to a pulley, and Block B is hanging from the pulley via cord.]

    2. Relevant equations

    F=ma

    3. The attempt at a solution

    This is embarrassing. I feel like I'm having a brain fart. I did free body diagrams showing that T-W_B=(M_A)a, and that T=(M_B)a, and substituted them into equations, but the book says it's the wrong answer; I should be getting 4.02 ft/s^2, but I'm getting something different. Any help please?
     
  2. jcsd
  3. May 10, 2012 #2

    PhanthomJay

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    You ll have to attach the pic or better describe the setup. 3 pulleys? What side is rod connected? How many ropes?
     
  4. May 10, 2012 #3
    Here you go.
     

    Attached Files:

  5. May 10, 2012 #4

    PhanthomJay

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    I don't know what answer you are getting, but your signage is wrong when looking at
    Block B. also make sure your mass unit are in slugs.

    Edit: you also used M_B in your second equation when you should have used M_A.
     
    Last edited: May 10, 2012
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