# Truss - Method of Joints in terms of load P

1. Oct 21, 2012

### opensourcery

Hello guys. I would like someone to check that I am doing this problem correctly. The answer given in the book is 0.577(P) for FAB and FAE which differs from the answer I get.

1. The problem statement, all variables and given/known data
Determine the force in each member of the truss in terms of the load P and state if the members are in tension or compression.
Drawing with work http://imagebin.org/232748 [Broken]

2. Relevant equations

$\Sigma$MA = 0
$\Sigma$Fx = 0
$\Sigma$Fy = 0

3. The attempt at a solution
Entire truss system

$\Sigma$MA = 0
-L(P) + 2(L)(Dy) = 0
Dy = $\frac{P}{2}$

$\Sigma$Fx = 0
Ax = 0

$\Sigma$Fy = 0
Ay - P + Dy = 0
Ay = $\frac{P}{2}$

Forces at pin A

$\Sigma$Fy = 0
Ay - $\frac{1}{\sqrt{2}}$(FAB) = 0
FAB = $\frac{\sqrt{2}}{2}$(P)

$\Sigma$Fx = 0
-$\frac{1}{\sqrt{2}}$(FAB) - FAE = 0
FAE = $\frac{-P}{2}$

Last edited by a moderator: May 6, 2017