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At What Angle Will This Box Begin to Slide?

  1. Jan 23, 2016 #1
    1. The problem statement, all variables and given/known data

    IMG_9759.jpg
    2. Relevant equations
    ΣFx=max

    3. The attempt at a solution
    IMG_9760.JPG

    I drew a free body diagram for the box and set up the equation to solve for θ, but I'm not sure how to do it without μ
     
  2. jcsd
  3. Jan 23, 2016 #2

    Suraj M

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    Gold Member

    I don't think you need to substitute
    ##F_{friction}## with ##μ F_N##
    They want you to use the frictional force they themselves have provided in the question.
     
  4. Jan 23, 2016 #3
    Oh my goodness I can't believe I missed that...... Thank you!

    ΣFx=max
    mgx-Ffx=max
    mgsinθ-Ffx=max
    (100)(9.81)sinθ-490.5=(100)(0)
    981sinθ=490.5
    θ=sin-1(490.5/981)
    θ=30°

    Wow, that was an embarrassing mistake!
     
  5. Jan 23, 2016 #4

    SammyS

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    Gold Member

    In a way, your mistake is one that is reasonable to make.

    In an actual situation, the friction force does depend upon the normal force, which depends upon the angle the surface make with the horizontal.

    Having the friction force be a fixed value, is not realistic.
     
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