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Static Friction Question

  1. Feb 11, 2008 #1
    I'm having trouble with this one problem, I've tried everything with my given notes, but the right answer isn't coming up:

    A block with a mass of 3.7 kg is placed at rest on a surface inclined at an angle of 52 degrees above the horizontal. The coefficient of static friction between the block and the surface is 0.40, and a force of magnitude F pushes upward on the block, parallel to the inclined surface. Calculate Fmin and Fmax.

    For Fmax, I got 8.9, (had to report to 2 sigfigs), by using the formula fs,max = mu(static coefficient) x N. N = mgcos(theta). My answer was wrong. Please, if anyone can help me find how to do this, it would be greatly appreciated!
     
  2. jcsd
  3. Feb 11, 2008 #2

    G01

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    I think your problem is in the fact that the applied force is in the horizontal direction. Consider the fact that only the component of F along the hill can act against the static friction force. So, when considering the relationships between friction and the maximum and minimum values for F, you are only going to want to consider the component of F along the hill. Do you see how this will change the relationships you are using?
     
    Last edited: Feb 11, 2008
  4. Feb 12, 2008 #3
    No, applied force is paralel to the slope. He forgot to take into account the component of gravitational force, that is paralel to the ground.
     
  5. Feb 12, 2008 #4
    Yo forgot to add the additional force acting in the parallel dimension of the gravitational force which will be (sin(52))(36.26) and then you would add that to your 8.9 and get 37.5 Newtons
     
  6. Feb 12, 2008 #5

    G01

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    Wow yes, you are correct. I don't know what I was thinking here... I must have read the problem incorrectly. I'm sorry for any confusion I caused.
     
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