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Homework Help: Yet another two-block system question. I guess I don't understand this still.

  1. Mar 8, 2010 #1
    1. The problem statement, all variables and given/known data
    See attempt at solution. It has everything.


    2. Relevant equations
    F_net = ma (net force)
    W = mg (weight)
    f_k = u_k * N (frictional force - kinetic)

    T is the tension force.

    3. The attempt at a solution

    See attachment below. I realize I just posted a problem related to a two block system. I got help on the last problem and thought I understood it completely, but this time I'm REALLY not sure what I'm missing. I checked over the coordinate system and all the signs in the problem and thought all my steps made sense. Am I simply missing a force?

    The answer I should be getting is u_k = 0.25, but I get 0.583 instead.
     

    Attached Files:

    Last edited: Mar 8, 2010
  2. jcsd
  3. Mar 8, 2010 #2

    rl.bhat

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    Homework Helper

    For 10 kg block g*sinθ and ax are in the same direction. So in that equation you have to equate it to -m*ax.
     
  4. Mar 8, 2010 #3
    Thank you, that did give me the correct answer. Are you saying the acceleration should be negative on block A since it is traveling in the -x direction (left)?
     
  5. Mar 8, 2010 #4

    rl.bhat

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    The mass is moving in the direction of g*sinθ. In the equation you have taken g*sinθ -ve, so ax also -ve.
     
  6. Mar 8, 2010 #5
    What is "ve"?

    EDIT: Nevermind, you mean -ve = "negative" haha. I'm a little slow tonight, nevermind! I understand, thanks.
     
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