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Homework Help: Forces and the Laws of Motion HELP

  1. Oct 2, 2007 #1
    Forces and the Laws of Motion HELP!!

    1. The problem statement, all variables and given/known data
    A 4.00 kg block is pushed along the ceiling with a constant applied force of 85.0 N that acts at an angle of 55.0 degrees with the horizontal. the block accelerates to the right at 6.00 m/s2. Determine the coefficient of kinectic friction between the block and ceiling.

    2. Relevant equations
    uk= Fk / Fn

    3. The attempt at a solution
    uk= Fk / 85.0 N
    sin 55 = x/85
    uk= 69.6/85 = .82
    the coefficient of kinetic friction between the block and the ceiling would be .82??

    is that right??

    i know this is too much to ask, but can anyone PLEASE explain to me forces and laws of motion.?? pleaseeee. i need major help about these especially with problems that have the angles and coefficient of friction..

    thankss :D
    1. The problem statement, all variables and given/known data

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. Oct 2, 2007 #2


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    Staff Emeritus
    Science Advisor
    Gold Member

    In questions like this all you need to know is pythagorean theorem for finding the magnitudes of resulting forces and trigonometry for resolving forces.

    First of all you need to resolve your force into the horizontal and vertical components using the magnitude of the force and the angle given. The normal force will of course be the vertical component. The horizontal component accelerates the block but is counteracted by the kinetic friction force. You can work out the force needed to accelerate the block at 6ms-2 and compare it to the horizontal component of force to find the kinetic friction force.
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