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Static Friction Ladder Problem

  1. Nov 11, 2011 #1
    1. The problem statement, all variables and given/known data
    See attachment.


    2. Relevant equations
    F = μN

    3. The attempt at a solution
    I attached the FBD I drew. I then did
    ƩFx = FA + FBcosθ - NBsinθ = 0
    ƩFy = NA -W + NBcosθ + FBsinθ = 0
    ƩMA = 19.5NB - 3.75W = 0
    ƩMB = 3.75W - 7.5NA + 18FA = 0
    FA = μNA
    FB = μNB
    θ = arctan(18/7.5) = 67.38°

    I know μ is supposed to equal .18, but I can't get it. I've tried substituting different things I don't know how many times now, and I can usually get to an expression of just μ or μ and θ, but I can never get it to equal .18.
     

    Attached Files:

    Last edited: Nov 11, 2011
  2. jcsd
  3. Nov 11, 2011 #2

    BruceW

    User Avatar
    Homework Helper

    The angles at the wall are wrong on your FBD. They should both be 90-theta.
     
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