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Another law of motion question, last one i swear

  1. Dec 11, 2006 #1
    another law of motion question, last one i swear!!

    1. The problem statement, all variables and given/known data
    a 2.00kg block is held in equilibrium on an incline of angle 60deg by a horizontal force F applied in the direction ->. If the coefficient of static friction between block and incline is .300, determine a) min value of F and B) normal force exerted by the incline on the block.


    2. Relevant equations
    ??


    3. The attempt at a solution
    Thats why i'm here, i need guidance, the book doesn't really cover this!
     
  2. jcsd
  3. Dec 11, 2006 #2

    radou

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    Homework Helper

    Draw a free body diagram for a start.
     
  4. Dec 11, 2006 #3
    [​IMG]

    here is the FBD that i drew
     
  5. Dec 11, 2006 #4

    OlderDan

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    Science Advisor
    Homework Helper

    Your F is not in the right direction. You have not shown the other forces acting on the block. You need three more forces.
     
  6. Dec 12, 2006 #5
    The most common mistake when drawing free-body diagrams is forgetting Newton's Third Law. Go back to the basics: every force must have an equal and opposite force. Also slelect your system correctly and understand the nature of constraining forces exerted by rigid bodies. Maybe you should study the chapter on Newton's Laws from some good introductory book like Halliday and Resnick (Not Walker).

    You haven't read the question carefully either, you have made a mistake in the drawing. As for equations, I'm sure your book covers the few necessary ones:

    The law of static friction ([itex]F_{lim} = \mu N[/itex]) and Newton's Second Law ([itex]F_{net} = Ma[/itex]). You will also need some basic vector algebra. Concentrate and draw another diagram.

    Molu
     
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