Engineering Question about Truss Analysis (Statics)

AI Thread Summary
The discussion revolves around a civil engineering student's confusion regarding truss analysis in a statics class. The student questions the correctness of a joint marked as valid, arguing that the equilibrium equations suggest that certain members should not be zero. Specifically, they analyze the forces at a joint, concluding that the member connecting joints 8 and 9 cannot be a zero-force member based on their calculations. The student expresses doubt about the accuracy of the solution provided by their teaching assistant. Overall, the inquiry highlights the complexities of understanding force systems in truss analysis.
ktw
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Homework Statement
Whoops.. accidentally wrote everything in the solution box! Please see below.
Relevant Equations
Fx=0, Fy=0
Hi, I am a civil engineering student currently taking Statics. We are doing truss analysis in the class right now; and I know that this joint is marked as correct.
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However, I don't see how this is even possible. I begin by considering this a concurrent 2D force system, Fy = 0 & Fx = 0. The equilibrium equation for Fy is -P + (1/√5)√5 * P + (1/√5)T = 0 ; where sin(θ) = (1/√5) and T is the diagonal that is following the line 8->5. I do not understand how the value of T can equal zero and then the member connecting joint 8 to joint 9 can also be zero; considering this would imply that (2/√5)√5P + 0 = 0 using the equilibrium equation Fx = 0. I understand zero force members and I do not think member 8->9 can be visually determined to be zero. Could anyone shed some light on this for me?

Thanks, Kyle
 
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Looking at this closely.. there's no way that the solution is correct. My TA must have been mistaken. Thanks for looking at my question
 
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