How do I solve internal force problems in statics?

AI Thread Summary
The discussion revolves around difficulties in solving internal force problems in a Statics assignment. The user is struggling with multiple questions, specifically focusing on creating accurate free body diagrams and identifying unknown forces. They express confusion about the number of equations available compared to the unknowns in their problems, particularly regarding reaction forces and internal forces at specific sections. The user seeks guidance on how to approach these problems, emphasizing a need for clarification and a starting point. Overall, they are looking for assistance to complete their assignment before the deadline.
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Please Help! Internal Forces in Statics

I have been attempting to answer the problems on my Statics assignment for about a week now but I have not been so success full. I have only be able to answer on of the problems the other three below I get stuck on. Can someone please help me get past the areas where I get stuck?

The first question that I'm having trouble with can be found by following the link below
http://herograw.com/7-20.JPG

My free body diagram looks like: http://herograw.com/fbd7-20.JPG

I'm not sure if that is the right the free body diagram and I am unsure as to how I can find the that largest virtical force. I'm wondering if I should leave the cable in the free body diagram that way its interaction is internal to the system and only have three unknown to find using \Sigma F_x = 0, \Sigma F_y = 0, \Sigma M_A = 0. Then I could go onto finding the internal normal force, shear force, and moment at the section C after I make free body diagrams for the section.

The second question is: http://herograw.com/7-32.JPG

My free body diagram is:http://herograw.com/fbd7-32.jpg

In this question I am comming up with four unknowns (Ax, Ay, Cx, and Cy), but I only have 3 equations to use (\Sigma F_x = 0, \Sigma F_y = 0, \Sigma M_A = 0). I don't think member AB is a two force body because there is an applied load acting on it. I'm not sure as to what I should do finish this problem. I need to know what the reaction forces are before I can find the internal forces acting at the section point D.

Lastly:http://herograw.com/7-40.JPG

This question confuses me. Could someone please clarify some as to what I need to do solve this question. I'm not sure how to make my free body diagram. I need a starting point and I can't seem to find one on my own.

Someone please help. I have to get this done before Tuesday. I thank all who can help in advanced.
 
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No one has any idea! I guess these questions are very difficult. Is there anyone who can help me in the least bit?
 
:bugeye: I guess there is no hope after all... :cry: :mad: :frown:
 
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