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Homework Help: HELP Tension/Friction Question

  1. Jan 25, 2007 #1
    A block of mass M resting on a 19.1° slope is shown. The block has coefficients of friction μs=0.788 and μk=0.482 with the surface. It is connected via a massless string over a massless, frictionless pulley to a hanging block of mass 1.86 kg. What is the minimum mass M1 that will stick and not slip?

    http://capa.physics.mcmaster.ca/figures/kn/Graph08/kn-pic0836.png [Broken]


    In terms of mass 1, following eqn can be written:

    m1g sin 19.1 - T - Ff = 0

    which can be rewritten as:

    m1g sin 19.1 - T - m1g cos 19.1 (friction coefficient) = 0
    right? since the object is at rest.
    then i found T by equating it to m2g (T = m2g...see the diagram as to why i have donet this)

    Hence m1g sin 19.1 - m2g - m1g cos 19.1 (0.788) = 0
    and then solved for m1....but im not getting the right answer
    I dont understand why my approach is wrong...where did i go wrong here?
     
    Last edited by a moderator: May 2, 2017
  2. jcsd
  3. Jan 25, 2007 #2
  4. Jan 25, 2007 #3
    plz help, much appreciated
     
  5. Jan 25, 2007 #4
    Plx

    im literally bursting into tears right now, plz
    this question has been frustrating me for the last couple of days
     
    Last edited: Jan 25, 2007
  6. Jan 25, 2007 #5
    ppl dont be so cruel, please!!!!!!!!!!11
     
  7. Jan 25, 2007 #6
    I've posted my solution and clearly demonstrated my attempt to resolve this question to no avail.

    PLZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZ
    i beg you, you can have my undying gratitude
     
  8. Jan 25, 2007 #7
    Apparently, you mess up the sign in Ff. When you are pulling the mass 1 uphill with tension T, the friction force shall point to the opposite to T.
     
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