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Homework Help: Incline plane - Did I do this right?

  1. Dec 13, 2004 #1

    tony873004

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    This is just a question I made up because there'll probably be one like this on our final exam.

    A 5 kg block is on an incline plane of 50 degrees. coeffecient of friction is 0.5. Will it slide?

    N = mg cos(50)
    N = 31.529
    friction = mu * N
    friction = 15.764

    force down = ma

    f =m g cos(50)
    f = 31.529

    force down > friction so it will slide.
     
  2. jcsd
  3. Dec 13, 2004 #2

    Pyrrhus

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    Actually the force making it slide it's the x component of gravity [itex] mg \sin \theta [/itex]

    and yes if [itex] mg \sin \theta > \mu mg \cos \theta [/itex] then it will slide.
     
  4. Dec 13, 2004 #3

    tony873004

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    Thank you...
     
  5. Dec 13, 2004 #4

    Pyrrhus

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    Why don't you try finding the coefficient of friction that will avoid the system from sliding or finding the angle it will not slide an a specific coefficient of friction? Those are some of the common problems asked.
     
  6. Dec 13, 2004 #5

    tony873004

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    if it slides when mg sin theta > mg cos theta, then when they equal that should be the minimum mu necessary to keep it from sliding.
    mg sin theta = mu mg cos theta
    mu = (mg sin theta) / (mg cos theta)

    but this gives me an answer greater than 1.
     
  7. Dec 13, 2004 #6

    Pyrrhus

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    Because the inequality says [itex] \tan \theta > \mu [/tex] that's why you are getting a greater value.
     
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