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Homework Help: Mechanics -- Object sliding again with friction

  1. Oct 16, 2014 #1
    1. The problem statement, all variables and given/known data
    first of all- yes,i looked in to similar topics,did not succeed :(

    My problem : The objects slides down on a plane which located 45degrees with respect to surface. It slides s=0.36m down, it reaches v=2m/s. I have to calculate the coefficient of friction.

    2. Relevant equations

    3. The attempt at a solution

    There is image( sorry for some reason, i could not upload it directly to here)

    http://postimg.org/image/uof2i65zv/ [Broken]

    So the friction coef. F_friction=(mu)*F_reaction -> (mu)=F_f/F_r
    From image above, its easy to see,that tan(alpha)=mu,so it seems too easy.

    And what for i need s and v values? I suppose it could be because i just calculated the static friction ,not the dynamic,yes? If i should calculate the dynamic one,could someone help ,please?
    Last edited by a moderator: May 7, 2017
  2. jcsd
  3. Oct 16, 2014 #2


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    I think that you should start with a clear sketch of the inclined plane, with the sliding object and the forces involved... I've seen your image, and it doesn't seem clear to me...
  4. Oct 16, 2014 #3
    I cant imagine what can i ad, there is Force of friction,reaction and mg, corresponding counter forces..
  5. Oct 16, 2014 #4


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    The essential vectors that you should draw clearly are:

    1) The weight mg
    2) One of its components, normal to the plane
    3) The other component, parallel to the plane
    4) The friction force.
  6. Oct 16, 2014 #5
    http://postimg.org/image/6ztyvaf4r/ [Broken]

    F_F is the friction force.
    And now there is components of mg!
    Last edited by a moderator: May 7, 2017
  7. Oct 16, 2014 #6


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    You should list those forces, one by one, as functions of mg. Then, write down the expression of the net force along the plane.

    After that, you should ask yourself: does the object accelerate in his sliding motion? And by how much?

    There may be other approaches to the problem, of course. That's just my way of solving it, that I believe correct...
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