Statics Question Moment for a Truss

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Discussion Overview

The discussion revolves around calculating the moment about point G in a statics problem related to a truss. Participants are attempting to solve a homework question involving forces and moments, with a focus on the correct application of the moment equation.

Discussion Character

  • Homework-related

Main Points Raised

  • One participant presents their calculation for the moment about G, leading to a value of A = 621 N, but expresses uncertainty about the correctness of this result.
  • Another participant suggests considering the moment produced by both components of a specific load, indicating a potential oversight in the initial calculations.
  • A different participant modifies the moment equation to include additional terms, resulting in a new calculation that yields 821 lb, but still indicates a discrepancy from the expected result.
  • One participant acknowledges a mistake in their approach, stating "wrong way its 20 thank you!" without further elaboration.

Areas of Agreement / Disagreement

Participants do not appear to reach a consensus, as multiple calculations yield different results and there is ongoing uncertainty regarding the correct approach to the problem.

Contextual Notes

There are indications of missing assumptions regarding the forces and moments involved, as well as potential confusion over units (pounds vs. Newtons). The calculations also depend on the correct interpretation of the forces acting on the truss.

baird.lindsay
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Homework Statement



I need to find the moment about G. Please ignore the question in the image.

http://img13.imageshack.us/img13/6086/4cv0.jpg

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Homework Equations



r X F

The Attempt at a Solution



Moment about G = -(30*800) + (-300*50) + 60 A + 17.32*500 + (-17.32*500(4/5)) =0

I keep getting A= 621 N but my solution is saying 721N. I am doing something wrong, not sure what.
 
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You need to look at the moment produced by both components for the 500 lb load at point I.

The reaction at A should be in lbs rather than Newtons.
 
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Moment about G = -(30*800) + (-300*50) + 60 A + 17.32*500 + (-17.32*500(4/5)) + (-40*500(3/5)) =0

When I do that I get 821lb? I am still off...
 
wrong way its 20 thank you!
 

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