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Homework Help: Finding the pushing force needed to keep object from sliding down wall

  1. Oct 15, 2011 #1
    This problem has been bugging me, seeing that my answer seems off. But who knows. Given the following measurements, find the required pushing force needed to keep a book from sliding down the wall.

    1. The problem statement, all variables and given/known data
    M= 2.88kg
    Coefficient of static friction= .322


    2. Relevant equations
    Seeing that the book can't move, I figured that F=Normal force
    mg=2.88kg(9.80 m/s^2)=28.2N
    force of static friction=μsN

    ƩFx=F-N=0
    meaning F=N (Makes sense)

    ƩFy=mg-fs=0
    meaning mg=μs(N)
    thus, N=(mg/μs)




    3. The attempt at a solution
    I did a simple substitution by setting F=(mg/μs)=(28.2N/.322)=87.6N

    To me, that answer seems a little high. So, is my reasoning and/or answer correct?
     
  2. jcsd
  3. Oct 15, 2011 #2
    The answer must be greater in magnitude than the weight of the book because friction coefficient < 1. Your answer looks good to me.
     
  4. Oct 15, 2011 #3
    That's good to know. Thanks.
     
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