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Homework Help: What is the coefficient of friction question?

  1. Dec 1, 2009 #1
    1. The problem statement, all variables and given/known data

    a boy uses a rope to pull a box weighing 300 Newtons across a surface with a constant velocity . The rope makes an angle of 30 degrees with the horizontal, and the tension in the rope is 100 Newtons. What is the coefficient of friction ??

    3. The attempt at a solution

    300 newtons - 100 newtons = 200netowns

    200 newtons x Cos30 = 173 ???

    is this the correct way to go about it ???
  2. jcsd
  3. Dec 1, 2009 #2
    Re: friction

    Well the easiest way to solve these kind of problems is to draw out a free body diagram. The thing to know about friction is that it only opposes the force parallel to the motion. Since the rope is at a 30 degree angle, the horizontal applied F= (100N)cos(30) = 86.6 N.
    Now since the box is moving at constant speed the Force of friction must be equal to the applied force. So Ff = 86.6 N in opposite direction. Then you must know Ff = umg where mg is the weight. 86.6N = u(300N) and solve for the coefficient of friction
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