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Homework Help: Tension and acceleration

  1. Feb 14, 2010 #1
    1. The problem statement, all variables and given/known data

    A light rope is attached to a block with mass 4.40 kg that rests on a frictionless, horizontal surface. The horizontal rope passes over a frictionless, massless pulley, and a block with mass m is suspended from the other end. When the blocks are released, the tension in the rope is 18.5 N

    2. Relevant equations

    newtons 2nd law

    3. The attempt at a solution

    T - m(g) = ma

    18.5 - 4.4(9.8) = 4.4(a)

    a = 5.59

    This is wrong?

    Help please!!

    thank you :)
  2. jcsd
  3. Feb 14, 2010 #2


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    I gather you are trying to find the acceleration of the blocks....when you draw a free body diagram of the block on the table, what are the forces acting on the block in the X direction? Then use F_x_net = ma
  4. Feb 14, 2010 #3
    i had to draw 2 free body diagrams for the first 2 parts of the assignment for the 4.4 kg mass and the unknown mass but i got them both wrong.... :(

    but the forces in the x direction acting on the block of mass 4.4 kg would be the tension and that is it right?
  5. Feb 14, 2010 #4


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    Right. That's the only force acting in the x direction. Ther are also forces in the y direction, 2 of them in the y direction. Can you identify them and their directions?
    When you draw free body diagrams, identify all the forces acting. The force of gravity is usually one of them, acting down toward the center of the earth. This is an 'action at a distance' force; almost all other forces in Physics 101 are contact forces...there must be a contact between 2 surfaces or particles or objects in order for there to be a force.
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