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Homework Help: The laws of Motion

  1. Sep 17, 2012 #1
    1. The distance between two telephone poles is 50.0 m. When
    a 1.00-kg bird lands on the telephone wire midway between
    the poles, the wire sags 0.200 m. (a) Draw a free-body diagram
    of the bird. (b) How much tension does the bird produce
    in the wire? Ignore the weight of the wire.

    2. this problem was from the laws of motion section. dealing with tension and f=ma

    3. i need help with beginning the problem. any suggestions.

    so i drew the free body diagram. so would t1 = t2 make the tension the same for both sides? and i found the weight of the bird which is 9.8 N. so where do i go from here to find the tension?
    Last edited: Sep 17, 2012
  2. jcsd
  3. Sep 17, 2012 #2


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    Homework Helper
    Gold Member

    You have enough information to make a sketch of the situation--do that first. Since it is a massless wire, assume initially that the unloaded wire is perfectly straight with no initial tension.
  4. Sep 17, 2012 #3
    After you draw the FBD, the weight of the bird would cause the wire to drop a bit and create an angle from the original horizontal position.

    Yes, the tensions are exactly the same. But you first need to find the horizontal and vertical components of the tensions (you only have to do this once because the tensions are the same).

    In the vertical direction, you know that the bird is exerting a force downwards equal to 9.8N, and so the tensions of the wires must add together to exert a force upwards equal to 9.8N. Because there are two separate tensions, each tension has a vertical component of 4.9N.

    See how far you can get with this.
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