Please see the link below for the question. I think Ax should be negative (not p

Question

Please see the link below for the question. I think Ax should be negative (not positive as shown in the solution in the link below)

https://www.chegg.com/homework-help/questions-and-answers/truss-loaded-supported-shown-identify-zero-force-members-b-use-method-sections-find-forces-q1591816?hwh_cr=1

400 lb F 840 lb 5.0 ft 5.0 ft 5.0 ft A 12 12 t 24.0 ft 24.0 ft 24.0 ft For the truss loaded and supported as shown, a) Identify all zero force members. b) Use the method of sections to find forces in members CF, CG and DG. Specify tension or compression, IT) or (C).

Explanation / Answer

Now i can't upload the image file.....so i can't provide the free body diagrams.....but the i can give the equations to solve

a) The zero force members are BD,GH,CE,EF,CD

B) By writing the equilibrium equations for the main diagram

forces in x direction............Ax-I*cos75=-840

forces in y direction ..........Ay+I*sin75=400

Moment about A point....I*0.96*72=(400*24)+(840*10)

I=260.41 lb , Ax= -774.81lb , Ay=-150 lb

Now by using method of section, cutting through members CF,CG AND DG

and for the section

forces in y direction......Ay-400-CG*0.38=0 ................CG=-1447.36 lb ..it is negative ..which means it is in tension

moment about a...CF*10+(400*24)+(0.92+0.38)*CG............CF= -771.84 lb ....It is also in tension

forces in x direction....Ax+DG+CF+CG=0......DG= 2994 lb ...it is in compression

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