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Homework Help: Application of Newton's Laws of motion

  1. Feb 26, 2007 #1
    A block of mass 20kg is pushed against a vertical surface at an angle of 30 degrees as shown. The coefficient of friction between the surface and the block is 0.2. What is the minimum magitude of P to hold the block still?


    I got 271.5 when I tried but the answer is 202.2
     

    Attached Files:

  2. jcsd
  3. Feb 27, 2007 #2
    How did you come to the 271.5?
     
  4. Feb 27, 2007 #3
    Have you taken into account the fact that the frictional force will depend also on P, ie how strongly it is being pressed against the wall?
     
  5. Feb 27, 2007 #4
    I came up withthe equation

    mg+ Fr = mg cos theta
     
  6. Feb 27, 2007 #5
    That equation does not look right. Where is P?

    Also how do you determine Fr. You need another equation right?
     
  7. Jan 30, 2012 #6
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