Statics 6.37 - Determine the force in members EF, BE, BC and BF of the truss. Tension or compression

Question: Determine the force in members EF, BE, BC and BF of the truss and state if these members are in tension or compression. Set P1 = 9kN, P2 = 12kN, P3 = 6kN.
Problem 6-37 from:
Engineering Mechanics: Statics, 14th edition
Russell C. Hibbeler
Thank you guys for watching.
Please let me know if you have any comments or suggestions and also if you have any other problem you would like to go over with.

[@danielbarela3154]

Thank you for explaining. You made it very easy to follow!

[@LearningbyTeaching]

I am happy to help!

[@kemalsogut9342]

Thank you sir!

[@timothysands5537]

Dangit, forgot the distance of F_D from point A for the moment balance. Hate it when you get all concepts right but make an arithmetic error lol.
THANKYOU for the video bro, very helpful walkthrough and good color coding.

[@LearningbyTeaching]

Hey that means you are learning the subject, we all make math mistakes. Keep it up!

[@Shardus_Blunder]

Thank you

[@Ozubura]

Why isn’t P3 counted when you are ∑MB=0 but F_EF is? That’s the only part that confuses me with method of sections: how can you count one unknown force at a point (this case point F) but not another in your equation of equilibrium? I understand that F_EF is within the section a-a and P3 is outside of it but they both affect the same point, which is also outside of section a-a.
Besides that question, thank you for these videos! They helped me understand moments of inertia before my mechanics final. Coming from a ChemE student stuck having to take mechanics as a general requirement.

[@LearningbyTeaching]

Hello, so you mentioned the reason and is that F_EF is within the section a-a but P3 is not. To better understand this, the point does not matter if its inside the section or not, because it is just an arbitrary point we decide to chose. Another way of seeing this is that F_EF is accounting already P3 in some sense and also the other internal forces of each of the members we are cutting thru.

[@uzairhussain8523]

Bro -fbesinø in horizontal
And -fbecosø in vertical
You did it opposite

[@LearningbyTeaching]

Hi, thanks for the comment. In this case since the angle was equal to 45 degrees then both sin and cosine are the same value.

[@maysonplaisted457]

He means that you drew the entire diagram the wrong way. fCF, not fEB. You have therefor not drawn the same diagram that is in the book, and answered a different question. You are right by your diagram, but not the same as in the book.@@LearningbyTeaching