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Homework Help: Statics: Varying Force

  1. Sep 22, 2008 #1
    1. The problem statement, all variables and given/known data
    The jib crane is designed for a maximum capacity of 10kN, and its uniform I beam has a mass of 200kg.
    a)Plot the magnitude R of the force on the pin A as a function of x through its operating range of x=0.2m to x=3.8m.
    b)Determine the minimum value of R and the corresponding value of x

    3. The attempt at a solution
    Totally stumped on this one. It'll be great if someone could point me in the right direction.
    I didn't even think the force would vary with distance :S. Isn't it only the moment about the point that changes? How do I determine the change in force with distance?
  2. jcsd
  3. Sep 22, 2008 #2


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    Science Advisor

    The pin can only resist force in the y-direction due to the definition of a pin. This means that the resultant force at the pin will be the sum of all the forces in the y-direction. Obviously there is a constant -10kN due to the load, however the resultant force in the y-direction at the cable will be a function of the position.

    Sum moments about the pin to get the vertical force in the cable. Then sum forces in the y-direction to get the force at the pin. Get three points to see if it's linear, if it is, then use the equation of a line.
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