Static Equilibrium Problem Dealing with Torque

  1. 1. The problem statement, all variables and given/known data

    The figure shows a model of a crane that may be mounted on a truck. A rigid uniform horizontal bar of mass = 90.00 kg and length = 5.200 m is supported by two vertical massless strings. String A is attached at a distance = 1.600 m from the left end of the bar and is connected to the top plate. String B is attached to the left end of the bar and is connected to the floor. An object of mass = 3000 kg is supported by the crane at a distance = 5.000 kg from the left end of the bar.

    Throughout this problem, positive torque is counterclockwise and use 9.807 m/s^2 for the magnitude of the acceleration due to gravity.


    Find the tension in string A.

    2. Relevant equations

    This problem lets you use hints and it suggested I use the following equation with having the Tension in String "B" as the origin.


    3. The attempt at a solution

    Tension A(1.6000m) - (90.00 kg)(9.807 m/s^2) 1/2(5.200 m) - (3000 kg)(9.807 m/s^2)(5.000 m) = 0

    I don't understand the "1/2" part in front of the length mass one. Is that because of where it is placed or its moment of inertia?
     

    Attached Files:

    Last edited: Mar 30, 2012
  2. jcsd
  3. PhanthomJay

    PhanthomJay 6,278
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    If the weight of the 90 kg beam is uniformly distributed over its length, where does its resultant load act?
     
  4. I'm sorry, I'm not sure what you mean by resultant load.
     
  5. PhanthomJay

    PhanthomJay 6,278
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    If a uniform beam that is 2 m long has a mass of 0.5 kg/m, its total mass is 1 kg and it's resultant or total weight is 9.8 N. It can be represented as a single force of 9.8 N acting at its center of gravity.
     
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