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Homework Help: Tension and force

  1. Jun 18, 2010 #1
    1. The problem statement, all variables and given/known data
    Assume the three blocks portrayed in the figure below move on a frictionless surface and a force F = 40-N acts as shown on the m = 3.0-kg block. p4_27alt.gif
    (a) Determine the acceleration given this system.
    (b) Determine the tension in the cord connecting the 3.0-kg and the 1.0-kg blocks.
    (c) Determine the force exerted by the 1.0-kg block on the 2.0-kg block.

    2. Relevant equations

    3. The attempt at a solution
    a. F=ma
    40N = (1kg + 2 kg + 3kg)a
    a=6.67 m/s2

    b. T=m(a+g)
    T= 6kg (6.67 m/s2 + 9.8 m/s2)
    OR (I tried both)
    T=4kg (6.67 m/s2 + 9.8 m/s2)

    c. F=ma
    F= 3kg(6.7 m/s2)
    F=20.1 N
  2. jcsd
  3. Jun 18, 2010 #2

    Doc Al

    User Avatar

    Staff: Mentor


    Not sure where you are getting g from in your equations. The only forces we care about here are horizontal.

    Hint: Analyze the forces acting on the 3 kg mass.

    Why 3 kg? Hint: Analyze the forces acting on the 2 kg mass.
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