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Homework Help: Friction and Incline

  1. Oct 12, 2008 #1
    1. The problem statement, all variables and given/known data
    The coefficient of static friction between the 3.00kg crate and teh 35.0 degree incline is 0.300. What minimum force perependicular to the incline must be applied to the crate to prevent it from sliding?

    Gravity = 9.80 m/s2

    2. Relevant equations
    Sigma Fx = Fcos(theta) + fs - wsin(theta) = 0
    Sigma Fy = n - Fsin(theta) - wcos(theta) = 0

    3. The attempt at a solution

    w = (3.00kg)(9.80m/s) = 29.4N
    n = .574F + 24.1N
    fs = .300(.574F + 24.1N) = .1722F + 7.23N
    Fx = .819F + 1.72F + 7.23N 0 16.9N = 0
    .991F - 9.67N = 0
    F = 9.75
    n = .574(9.75) + 24.0
    n = 29.6N

    Problem that I am running into is that the solution to the question is actually 32.1N and I can't see where I went wrong. Help would be much appreciated. Thank you.
     
  2. jcsd
  3. Oct 12, 2008 #2
    Anyone?
     
  4. Oct 13, 2008 #3

    alphysicist

    User Avatar
    Homework Helper

    Hi jstiel,

    I don't believe the Fcos(theta) and Fsin(theta) are correct in these equations. What do you know about the direction of the applied force? Do you get the right answer?
     
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