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Homework Help: Newtons Third Law Problem

  1. Oct 6, 2011 #1
    Figure shows a block of mass resting on a slope. The block has coefficients of friction and with the surface. It is connected via a massless string over a massless, frictionless pulley to a hanging block of mass 2.0 kg.
    i got this first one: What is the minimum mass that will stick and not slip?

    1.83 kg
    Correct

    But can't get the second part:
    If this minimum mass is nudged ever so slightly, it will start being pulled up the incline. What acceleration will it have?

    knight_Figure_08_36.jpg

    Thank you! :)
     
  2. jcsd
  3. Oct 7, 2011 #2

    ehild

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    Correct the sentence in red please. What are the coefficients of friction?

    ehild
     
  4. Oct 7, 2011 #3

    PeterO

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    Once the block starts moving, the coefficient of friction is then the kinetic coefficient, which will mean a smaller friction. Thus there is a net force up the slope [and down on the hanging mass] which causes the system to accelerate.
     
  5. Oct 7, 2011 #4
    I'm really sorry about that ehild! The mu(s) is .8 but the mu(k) which I assume we use on this problem because it's moving therefore kinetic is .5 =-)
     
  6. Oct 7, 2011 #5
    Thank you Peter!
     
  7. Oct 7, 2011 #6

    ehild

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    Everything is clear then. Can you solve the second part or still need help?

    ehild
     
  8. Oct 7, 2011 #7
    Yes, it's clear. Thank you ehild! :)
     
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