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Homework Help: Basic torque question.

  1. Apr 29, 2012 #1
    1. The problem statement, all variables and given/known data
    http://imgur.com/BqIoe

    There is a 50 meter bridge with two supports. The bridge has a mass of 80000kg. A truck of 30000 kg is 15m from one of the supports. What are the forces acting on the ends of the bridge?

    Answers in back are F_a(support closer to truck): 598000 N and F_b: 480000 N

    2. Relevant equations
    torque = Force_perpendicular * distance

    center of mass for uniform object is center of geometry

    3. The attempt at a solution
    Sum of Forces in y direction on bridge: = -80000g - 30000g + Fn A + Fn B = 0

    Torque @ A = -15(30000) - 25(80000) + 50*Fn B = 0
    Fn B = 490000

    Torque @ A = 35(30000) + 25(80000) - 50*Fn A = 0
    Fn A = 305000

    What am I doing wrong? Any help is appreciated.
     
  2. jcsd
  3. Apr 29, 2012 #2
    Bump? Anyone?
     
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