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Wire tension physics help

  1. Aug 15, 2005 #1
    Two wires support a beam of length L=20 m and mass 330
    kg as shown in the figure above. A box of mass 220 kg hangs
    from a wire which hangs from the beam a distance x=15 m
    away from the left edge of the beam. What is the tension in
    the RIGHT support wire? (in N)

    I just did an (at least I thought...) similar problem to this, and got the answer correct. For the life of me, I don't know why this would be different. This is what I've been doing..

    center of beam = 0 m, so

    10 m*(330/2 kg * 9.81) + 5 m*(220 kg * 9.81) = 10 m* x N

    the only difference is that the weight of the beam wasn't given in the question I got correct, and I was solving for the weight of box. :confused: why would this be different?
  2. jcsd
  3. Aug 16, 2005 #2


    User Avatar
    Staff Emeritus
    Science Advisor

    You are correct that the beam contributes a tension of (330/2 kg * 9.81 m/s2) on each wire suspending the beam.

    Check your moments. The sum of the moments is zero (statics). Look at the moments about the left side (left pivot).

    Also think about superposition. The beam is evenly distributed by the wires, the 220 kg box is not.
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