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Homework Help: What is the tension in the cord connecting the two blocks at this instant?

  1. Feb 24, 2010 #1
    1. The problem statement, all variables and given/known data

    The coefficient of static friction between block A and a horizontal floor is 0.45 and the coefficient of static friction between block B and the floor is 0.30. The mass of each block is 2.0 kg and they are connected together by a cord.

    What is the tension in the cord connecting the two blocks at this instant?
    Answer: N


    2. Relevant equations and 3. The attempt at a solution

    as the friction force on the block A is 8.82 N, for just to move it the force is 8.82 N and this is applied by the cord only. Hence the tension in the cord is 8.82 N

    T = 0.45 * 9.8 * 2 = 8.82 N => INCORRECT. Why??? Please help!
     
  2. jcsd
  3. Feb 24, 2010 #2

    tiny-tim

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    Hi huybinhs! :smile:

    At what instant? You haven't said what is happening to the blocks. :confused:
     
  4. Feb 24, 2010 #3
    Part a for this problem is "If a horizontal force F pulling on block B is slowly increased until it is barely enough to make the two blocks start moving, what is the magnitude of F at the instant they start to slide?"

    I already figured it out that the answer is 15.092 N.

    I dont know how to do part 2. Please help!
     
  5. Feb 24, 2010 #4

    tiny-tim

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    ahhh! :rolleyes:

    ok then, the acceleration of the second block is zero, so just balance the forces on the second block. :smile:

    (or the first block … same result … just takes a bit longer :wink:)
     
  6. Feb 24, 2010 #5
    Ok. Thanks! My answer is CORRECT, my instructor just fixed it. Thanks anyway ;)
     
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