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Homework Help: Force needed to support Suspension of a Vehicle

  1. Sep 20, 2015 #1
    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.


    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
    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. jcsd
  3. Sep 22, 2015 #2


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    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.
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