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Trying to find static friction

  1. Oct 6, 2008 #1
    1. The problem statement, all variables and given/known data

    [​IMG]

    3. The attempt at a solution

    i've tried

    u(mg+fcos(theta)
    u(mg+fsin(theta)
    u(mg+fsin(theta)

    they have all been wrong. before i guess using: u(mg-cos(theta) and risking missing more points, can you tell me if it's right and if not, what do i do to solve this problem.
     
    Last edited: Oct 6, 2008
  2. jcsd
  3. Oct 6, 2008 #2
    Forces in y direction = gravity, normal force and y component of applied force.
    To calculate static friction you can ignore the x plane (in this example).

    The magnitude of normal force is of course the y component of applied force + gravity.

    y componenet of applied force = 107sin(theta).

    Ffriction = u[mg + 107sin(theta)]
     
  4. Oct 6, 2008 #3
    yeah i forgot to put the f in the equations that i used. i used it and still got it wrong... ahh
     
  5. Oct 6, 2008 #4
    Could you please show exactly what you did..?

    0.67[(21.5)(9.81) + (107)(sin(35))] ?
     
  6. Oct 6, 2008 #5
    that is what i used but i found the answer. its 88.707 N

    apparently u just do fcos(theta)

    107cos34... i dont get it but im read over some notes on what exactly force of static friction is...
     
  7. Oct 6, 2008 #6
    Interesting, if the question is posing that the gravitational force down is cancelling out its equal and opposite component in the positive y direction, that would mean that if the applied force was horizontal, then there would be no static friction.
     
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