Force needed to support Suspension of a Vehicle

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1. Sep 20, 2015

Alison A.

1. The problem statement, all variables and given/known data
A model for the suspension of a vehicle is shown where the spring has stiffness k = 178 N/mm and an unstreched length of 347 mm.

http://imgur.com/1dTVs12

Determine the value P and the force supported by member AB so that the suspension has the equilibrium position shown where member AB is horizontal.

2. Relevant equations
ΣF=0
ΣFxi+ΣFyj=0,
ΣFx=0, and ΣFy=0.
Spring Law: Fs=kδ=k(L-L0)

3. The attempt at a solution
I started by trying to find the force of the spring
Fs= 178 N/mm (RCA-347mm)

Finding RCA I took the pythagorean theorem (141)2+(229)2=RCA, RCA=268

However when I put that number back into the equation it's a negative number... I don't understand why or what I'm doing wrong.

2. Sep 22, 2015

BvU

I think I saw this in another thread too ? Anyway, the force the spring exercises being negative says something about the direction it is working in. That's perfectly fine. Your problem statement says nothing about it, but I suppose the picture has AB horizontal and the car in a steady state equilibrium. Then your equations come in useful.