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EK 1001 physics #277

Discussion in 'MCAT Study Question Q&A' started by divinelyawesome, May 19, 2014.

  1. divinelyawesome


    Apr 3, 2014
    I'm geting confuse about the application of newton second law here:

    The plane above is inclined at a 60 degrees angle. The coefficient of static friction is 0.2. The mass is 100 kg. What is the minimum force F necessary to start the object moving up the plane? Basically, the object is being pulled up the incline by a cord. So we have:
    Sum of forces in x direction=T-f-W.sin(60degrees)=m.a
    In y direction:N=W.cos(60)
    a is zero in y direction, but I don't understand why it's zero in the x direction. If the object is moving upward, it has an acceleration. Should I assume it's moving at cst velocity?
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  3. syoung

    syoung MS-3 5+ Year Member

    Jan 2, 2011
    Over the rainbow
    If it's moving it doesn't mean it has acceleration. You need to look at all of your forces.
  4. DrknoSDN


    Feb 21, 2014
    In this question it would be accelerating but that isn't relevant. They gave you coefficient of static friction and at a certain force you will overcome that static friction and have less friction because the coefficient of kinetic friction is smaller.
    That's why the question asked at what minimum force will it break free of the kinetic friction and begin to move.

    Basically once it starts sliding it will continue sliding.
    This is true for just about every scenario with friction because kinetic is always smaller than static.
  5. divinelyawesome


    Apr 3, 2014
    Okay, I get it. Thanks guys.

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