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Coefficient of friction for a car sliding down an icy hill

  1. Sep 26, 2011 #1
    1. The problem statement, all variables and given/known data

    A car is sliding down an icy hill inclined at 1.6 degrees, find the coefficient of friction.


    2. Relevant equations

    f_k=\mu_k*n

    3. The attempt at a solution

    Don't know how to begin it only given the angle of the hill.
     
  2. jcsd
  3. Sep 26, 2011 #2
    Draw a free body diagram of the car. Mark all the forces on it. Then apply Newton's laws of motion.
     
  4. Sep 26, 2011 #3

    PeterO

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    Homework Helper

    If you do all the manths with component, you will find that the co-efficient of static friction is the tangent of the angle of the hill when the body is on the point of slipping.
    One problem with this question is we don't know if this is the smallest angle for which it will slip?

    If it slips at 1.6 degrees, it will certainly slip at 10 degrees, but did it slip and 1.5? 1.4? 1.3 ? ...

    Also I noted that your forumula had the subscript k - presumably meaning the kinetic [moving situation] If the car is sliding down the hill but NOT accelerating, then tan1.6 will give the co-efficient you seek. However, we are not told whether it is accelerating or not???
     
  5. Sep 27, 2011 #4
    PeterO is right. This problem cannot be solved without knowing the acceleration of the car.
     
  6. Sep 27, 2011 #5
    I'm sorry, I forgot to add that it's sliding at a constant speed. Should've copied it word for word.

    EDIT: Tangent of 1.6 gives the correct coefficient, thanks. I don't understand why though, going to read over the problem and your input.
     
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