Determine the Moment and the Maginitude of the Moment

  • #1

Homework Statement

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.

Homework Equations

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?


Answers and Replies

  • #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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