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Sliding coin

  1. Jan 20, 2014 #1
    1. The problem statement, all variables and given/known data

    (c) This coin is placed flat on the same ramp (incline of 50.0o to the horizontal) and released from rest. How fast is the coin moving after the same distance down the ramp (30.0 cm) if the coefficient of kinetic friction is 0.75?

    2. Relevant equations

    3. The attempt at a solution
    I'm not sure what is meant by the coefficient of kinetic friction.
  2. jcsd
  3. Jan 20, 2014 #2


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    Gold Member

    the coefficient of kinetic friction tells you how the surfaces (the coin and the ramp surfaces) interact. Start with a free-body diagram and show all the forces on the object. But maybe first you should read about friction and see how the coefficient of friction is used:

  4. Jan 20, 2014 #3


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    Staff: Mentor

    Seems like something you could look up in your notes, your text, or online via web search.
  5. Jan 20, 2014 #4
    There are two coefficients of friction - inertial and kinetic. In both cases, they are the ratio of the frictional force to the force pushing the two surfaces together.

    Generally, materials will have a higher coefficient when they are not sliding past each other. That higher coefficient is the "inertial" one. Once that inertial friction is overcome, the surfaces begin sliding past each other and the frictional force becomes "kinetic friction".
  6. Jan 20, 2014 #5


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    Staff: Mentor

    I think you mean "static", not "inertial". The two coefficients for the standard model of friction are:

    μs: coefficient of static friction
    μk: coefficient of kinetic friction
  7. Jan 20, 2014 #6
    Oh my God. I don't know why but whenever I read this question I read it as 'coefficient of kinetic energy' and I was getting really confused by it. That's embarassing :S
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