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Homework Help: I was set a question and need help

  1. May 25, 2006 #1
    My math teacher set me a question on friction, knowing I was interested in physics. But he never gave me the solution, So i'm not sure if my working is correct. Any help is appreciated.

    Question: A brick of mass 1.2 KG is sliding down a rough plane which is inclined at 25 degrees to the horizontal. Given that the acceleration is 0.3ms^-2, Find the coefficient of friction between the brock and the plane.

    My answer: Using F = ma

    R - 1.2g cos25 = 1.2 x 0
    R = 1.2g cos 25
    R = 10.66 N

    1.2g sin25 - F = 1.2 x 0.3
    F = 1.2g sin25 - 1.2 x 0.3
    = 4.61 N

    Therefore F = 'mu'R
    4.61 = 'mu' x 10.66
    4.61/10.66 = 'mu'
    'mu' = 0.43

    Many thanks, Alex
    Last edited: May 25, 2006
  2. jcsd
  3. May 25, 2006 #2
    looks ok to me, and the 0.43 would indicate a rather high friction which makes sense.
  4. May 25, 2006 #3
    Yay, Thanks for takin the time to read my post. :) Do you know of any sites which offer questions such as these with solutions, So I may practice more? Alex
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