# Homework Help: Method of joints trusshelp

1. Aug 21, 2008

### mikel lowery

Hi, im really stuck here. My problem is with determining the support reactions. I understand that this needs to be done first before working on each truss member. But I don't understand how to determine them. I have read and re-read all my available text and still stuck.

The question I can't solve, " Determine the force in each member" of the attached. Each joint are pin joints.

Can some one please walk me through this?

Regards

Mikel

<- Edit ->

I have tried to solve rather than just ask, i'm aware that the 3 laws of equilibrium apply for the reactions, sum of x =0, sum of y= 0 and sum of Mc = 0. I just don't understand 1. Where the reactions are and 2. how to determine them?

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Last edited: Aug 21, 2008
2. Aug 21, 2008

### merryjman

You picture hasn't been approved yet, but if this is a static equilibrium question, it sounds like a pretty classic problem. You can't solve it with just the sum of x and y forces because you have too many unknowns. But the torques also are balanced. So you can get a second system of equations and solve for the unknowns.

3. Aug 22, 2008

### mikel lowery

merryjman,
Thank you for your reply. I think I understand the theory, im just unsure of how to put together. How do I determine where the reactions are and find them?
Regards

4. Aug 23, 2008

### merryjman

Still can't view the picture, but I think this website will be helpful: http://physics.uwstout.edu/Statstr/Strength/StatII/stat22.htm

If your situation is similar to that, then you use Newton's 2nd to figure out where the reaction forces are, and the torque equations to eliminate some of your unknowns in the force equations. In the example on the website, there is a reaction force at the pin joint, for example.

Last edited by a moderator: Apr 23, 2017