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Homework Help: Tension Force?

  1. Oct 26, 2007 #1
    1. The problem statement, all variables and given/known data

    A strong plank 8.0 m long and having a negligible mass is supported by steel cables from both ends. A jaguar with a weight of 800 N stands 2.0 m from one end. What is the tension force in the cable farthest from the jaguar?

    a. 120 N
    b. 200 N
    c. 240 N
    d. 400 N
    e. 600 N
    f. 800 N

    2. Relevant equations

    3. The attempt at a solution

    I'm not sure how to solve this problem. Is it a two dimensional problem? I'm not told whether the bridge bends down because of the jaguar's weight. Now, to find the tension force, I know it's m times a, but since the jaguar is not moving, the jaguar's pull on the rope (the tension force) is only going to be the force of gravity which the jaguar experiences (in the -z direction). Is this then simply 800 N? But how do I take distances into account when calculating tension force? Thanks for any help.
  2. jcsd
  3. Oct 26, 2007 #2


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    Staff Emeritus
    Science Advisor

    The problem is one of statics.

    The sum of the tensions in the cables must equal that of the jaguars weight, but since the jaguar is asymmetrically positioned between the cables, one will bear more of the weight than the other.

    To find the distribution of forces between the cables, pick one end and use the requirment that the sum of the moments about a pivot must equal zero.

    Pick the end closest to the jaguar, and determine the moments. Take positive moment to cause counterclockwise rotation looking at the x,y plane.

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