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Static Equilibrium and Torque Homework Question

  1. Dec 18, 2011 #1
    1. The problem statement, all variables and given/known data

    A hiker, who weighs 985 N is strolling through the woods and crosses a small horizontal bridge. the bridge is uniform, weighs 3610 N, and rests on two concrete supports, one at each end. he stops one - fifth of the way along the bridge. What is the magnitude of the force that a concrete support exerts on the bridge:

    a) at the near end and
    b) at the far end

    Answer to a) 2590, b) 2010

    2. Relevant equations

    Static Equilibrium: ƩT = 0
    T = Frsinθ

    3. The attempt at a solution

    Took opposite support as pivot point such that Fn x r is the CCW torque where r is the length of bridge
    Expressed distance from the pivot point of each force in terms of r
    Wrote net torque equation, crossed out r from both sides
    Solved for Fn

    a) Fn = 985 x 4/5 + 3610 x 1/2
    Fn = 2593 N
    b) Fn = 985 x 1/5 + 3610 x 1/2
    Fn = 2002 N

    I am not sure whether or not my approach to this problem is correct.
  2. jcsd
  3. Dec 18, 2011 #2


    User Avatar
    Homework Helper

    Yes, looks good.
    You can also sum the vertical forces - total must be zero - as a check.
    2593 rounds to 2590, but I don't see how to get 2010 from 2002.
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