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Math Help - dynamics/equilibrium

  1. #1
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    dynamics/equilibrium

    A body of mass 10 kg, at rest on a rough horiz surface, is acted on my a force of magnitude 14 N acting at an angle of 30deg to the horizontal.
    If the body is on the point of moving, what is the coefficient of friction between the body and the surface?

    I'm sorta having trouble visuallising the problem. I tried, but i dont think i got anything like the multiple choices.
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  2. #2
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    Quote Originally Posted by scorpion007 View Post
    A body of mass 10 kg, at rest on a rough horiz surface, is acted on my a force of magnitude 14 N acting at an angle of 30deg to the horizontal.
    If the body is on the point of moving, what is the coefficient of friction between the body and the surface?

    I'm sorta having trouble visuallising the problem. I tried, but i dont think i got anything like the multiple choices.
    Resolve the force into components along and perpendicular to the plane, these are \sqrt{3}\cdot 14 N and 7N respectivly.

    The total force perpendicular to the plane is now 10g+7 N, and this is equal to the normal reaction, so the limiting static friction is \mu(10g+7), which from what we are told is equal to the force along the plane so:

    \sqrt{3}\cdot 14 = \mu (10g+7)

    or:

    \mu = \sqrt{3}\cdot 14 / (10g+7).

    RonL
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