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Homework Help: Blocks are connected by thin strings with tensions

  1. Jul 5, 2009 #1
    1. The problem statement, all variables and given/known data

    Four blocks are on a horizontal surface.

    The blocks are connected by thin strings with tensions Tx, Ty, Tz. The masses of the blocks are A=41.0 kg, B=21.0 kg, C=29.0 kg, D=39.0 kg. Two forces, F1=47.0N and F2=71.0N act on the masses as shown. Assume that the friction between the masses and the surface is negligible and calculate the tension Tz.

    2. Relevant equations


    3. The attempt at a solution

    I calculated the total mass =130 kg
    Total force 71-47= 24 N
    Then the acceleration F/m=0.1846 m/s^2
    Next I calculated the Tension in Tz by :
    Tz -F1 = 130 * 0.1846
    I got 70.9 N

    I'm not sure if that's correct??
  2. jcsd
  3. Jul 5, 2009 #2


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    Homework Helper

    Re: Tension

    Not quite. You have the acceleration of the system. That's a start.

    Now you need to figure the internal forces, you know like block 1 times acceleration is presenting a force, block 2 times acceleration ... etc. Then you can determine the tension in the middle cord.
  4. Jul 5, 2009 #3


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    Homework Helper

    Re: Tension

    Tz -F1 = 130 * 0.1846 It is not correct.
    From Ty -F1 = 29 * 0.1846 find Ty
    From Tz - Ty = 39 * 0.1846 Find Tz
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