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Tension Problem, with slope and 2 masses

  1. Oct 12, 2012 #1
    1. The problem statement, all variables and given/known data
    http://www.xtremepapers.com/papers/...S Level/Mathematics (9709)/9709_w10_qp_43.pdf number 3


    2. Relevant equations
    T=mg (no acceleration as equilibirum)
    sin rule?


    3. The attempt at a solution
    Not sure where to start..the marking scheme shows that sin/cos rules are used but I dont understand why they are used.
    At first i wrote that m1g=T, and m2gsin30=T. Therefore, resultant force on pulley is mqg+mwgsin30, but, this is a dead end
     
    Last edited: Oct 12, 2012
  2. jcsd
  3. Oct 12, 2012 #2

    Doc Al

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    Staff: Mentor

    Set up an equation for the net force that the strings exert on the pulley. You'll need to add vectors, so that's where those rules would apply.
     
  4. Oct 12, 2012 #3
    ok, so the resultant force is 2Tcos30 along AQ and AP? how can we say for sure the two angles are the same?
     
    Last edited: Oct 12, 2012
  5. Oct 12, 2012 #4

    Doc Al

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    Staff: Mentor

    How did you get that?
    What two angles?
     
  6. Oct 12, 2012 #5
    i assumed AP and AQ are hypotenuses to the line of direction of 3sqrt3. So, Tcos30 +Tcos30=3sqrt3?

    Since the angle is 30 degrees, the other angle on top is 60 degrees. I assumed that the angle is divided equally into 2?
     
  7. Oct 12, 2012 #6

    Doc Al

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    Staff: Mentor

    Ah, I see what you're doing. Yes, that's a fine way to add them up. You took advantage of symmetry, taking their components along the bisector of the 60° angle. Good!

    I think you meant: Tcos30 + Tcos30 = T√3

    (You can also use the law of cosines to add them up. Same answer, of course.)
     
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