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Introductory Torque Statics Problem

  1. Feb 9, 2015 #1
    1. The problem statement, all variables and given/known data
    You're carrying a 4.0-m-long, 24kg pole to a construction site when you decide to stop for a rest. You place one end of the pole on a fence post and hold the other end of the pole 35 cm from its tip.

    I've drawn a diagram of the problem on Paint...
    upload_2015-2-9_19-15-51.png

    2. Relevant equations
    ∑τ=0
    τ=F⊥r

    3. The attempt at a solution
    I know that ∑τ=F(r1)+w(r2)+N(r3)=0, and I'm going to rewrite it so F(r1)+N(r3)=-w(r2). Now, if I call the left-most point the pivot point, my new equation becomes F(.35m)+4m(9.8 N/kg * 24kg) =-2m(-9.8 N/kg* 24 kg), which simplifies to F(.35m) = -470.4Nm, which makes F=-1344N. This seems way too big to be right; what did I do wrong?
     
  2. jcsd
  3. Feb 9, 2015 #2

    lightgrav

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    Homework Helper

    it would be much easier to use the RIGHTmost point as the pivot. Where is the weight applied? ... why are you not adding torques to zero? ...
     
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