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Need help on Ramp Problem

  1. Nov 28, 2009 #1
    1. The problem statement, all variables and given/known data
    What is the minimum horizontal force that must be applied to the stationary 4.0kg block so that the block will start to slide up the ramp? the ramp is inclined at a 37degrees angle and the coefficient of static friction between the block and the ramp is 0.23.

    2. Relevant equations
    Ff = μN
    ---

    3. The attempt at a solution
    y-direction
    0 = N - mgcosθ
    N = mgcosθ
    N = 4(9.8)cos37 = 31.3
    ------
    x-direction
    0 = Fcos(θ) - Ff − mgsinθ
    F = (mgsinθ + Ff)/cos(θ)
    F = [39.2sin(37) + (.23(39.2)(cos37)]/cos37
    F = 38.6
    ==================================================
    I have the wrong answer because the correct answer is
    N = 59.4N, F = 46.6
    Also, i think the way i use to solve F is right but i believe my N is wrong because when i plug in the N of the correct answer i get the same F as the result. Hope you can help me solve this problem thanks a lot
     
  2. jcsd
  3. Nov 28, 2009 #2

    alphysicist

    User Avatar
    Homework Helper

    Hi Toila,

    Notice here that you have the x-component of the applied force. But you have not taken into account the y-component of the applied force anywhere.

     
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