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Homework Help: Determine the Moment and the Maginitude of the Moment

  1. Sep 26, 2012 #1
    1. The problem statement, all variables and given/known data
    The weight of the printer is 86 lb with center of gravity at point G. Determine the moment MOof this weight about point O on the horizontal table top. Find the magnitude of MO.

    2. Relevant equations

    3. The attempt at a solution
    My initial impression was to find the moments about the x, y and z axes and that these would give me their i, j and k components respectively

    Mx = (86 lb)(52")
    = 4472 lb-ft
    My = (86lb)(22")
    = 1892 lb-ft

    But I've compared these values to an identical question, with altered numbers, in my textbook and my values are much too large to be be the i and j components respectively (there is no k component because the force is parallel to the z axis). So what am I missing?

    Attached Files:

  2. jcsd
  3. Sep 26, 2012 #2
    Just found my mistake. I confused my units; the units given in the diagram are in inches, whereas the system and the example question want and give their answers respectively in feet. I converted the measurements in the diagram to feet and my answer is as follows:

    Mx = -(86 lb)(4.33 ft)
    = -372.6638 lb-ft

    My = (86 lb)(1.833ft)
    = 157.66638 lb-ft

    Mo = sqrt(372.6638^2 + 157.6638^2)
    Mo = 404.644 lb-ft

    These answers are correct.
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