# Finding the force exerted on a truss

## Homework Statement

Find the Force exerted on member ABCD by the pin at B in figure P4.162 (figure is attached)

## The Attempt at a Solution

This is also attached. As you can see I solved for everything I could. If I could solve for just one more unknown, I could solve the problem. I just don't see where I could possibly solve for any of them. Can anyone nudge me in the right direction?

#### Attachments

• 4.162.png
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• my work.jpg
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nvn
Homework Helper
Patdon10: Hint: Let your free body be bars BF and CE. The unknown external forces on this free body occur at points B and C. This free body has three equations, and three unknowns. You know the force in bar CE is axial.

What are the 3 unknowns? B_x, B_y, and then just C?

nvn
Homework Helper
Yes.

I'm having trouble getting a grasp on this, how do I know what direction C points in?

nvn
Homework Helper
You don't (or you do not need to know). However, you do know C is an axial force, like I said. Regarding whether it is tension or compression, you just assume a direction. Then if its numeric value, in the solution, comes out negative, you know you drew it backwards.

But what direction would it be? What are my options? because the pin connects to truss AD, does the direction have to go along that truss? or is it along it's own truss - meaning it would simply be up or down.

F_x = B_x - 1000 = 0
B_x = 1000N

Summation of Fy = B_y - C = 0
B_y = C

M_B = (-0.25)C + (0.73)(1000) = 0
C = B_y = 2920 N

Am I understanding this correctly?

nvn