Understanding Axial Forces and Section Properties in Strength of Materials

[stevie2869]

Homework Statement

I am having trouble with question 1 on the attachment posted. I understand that i need to get the area of the 2 bars. I am just not sure what to do with the forces. ALso i know the picture may be dark. P2 starts at point B and is pulling to the right and P3 starts at point C and is pulling to the left.

Homework Equations

I believe i use the equation A=∏d(^2)/4 to find the area but i am lost from there

The Attempt at a Solution

 

[OldEngr63]

Looks like this is a test question. Perhaps you should do this on your own?

 

[stevie2869]

Its Review for our final. Its an old test The question comes right out of our textbook.

 

[stevie2869]

after doing some research online i think i may be on the right track. The question is attchment #1 and my solution is attachment #2 .Please advise if i am doing this correctly. Thank you in advance

 

[kimann020]

I took that class last semester and you calcuations look correct to me, but then again i didnt ACE that class by any means

 

[pongo38]

3 things. Why do you use pi on what the question says is a square section?
Your units of stress are not what an engineer would use. Have you drawn a normal force diagram, that is, a graph showing variation of axial load from one end to the other and checked it. If you had, and included the reaction I think you wouldn't have made the mistake you have for the force in AC.

 

[stevie2869]

wow. I misread the question. I still believe i need to use the equation θ= P/A
but now I am not sure how to get the area of a square bar A= bh when only one dimension is given? I no whave no idea what my next step is. We have not covered normal force diagrams

 

[pongo38]

"im not sure how to get the area of a square bar A= bh when only one dimension is given?"
What do you understand is the difference is between a rectangular section bar and a square section bar? Do you have a working definition of the axial force at a section?
I have told you what a normal force diagram is. Can you sketch that by calculating the axial force at every section of the bar?