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Inclined planes stuck on someting

  1. Oct 3, 2013 #1
    1. The problem statement, all variables and given/known data

    2) In the variant of Atwood’s machine shown below, a mass slides on an inclined surface 40θ above the horizontal with a coefficient of kinetic friction μk = 0.15. The masses M1 and M2 are 1 kg and 2 kg, respectively. Which way does the pulley rotate? If the lowest point of each mass is initially 2m above the ground (vertically), and the system has a very small but non‐zero initial speed, how long does it take the first mass to hit the ground?

    2. Relevant equations
    F=MA



    3. The attempt at a solution

    So heres how I went about the problem. I first got a force diagram going and found all the forces

    F-parallel = 15.01N
    F-Perpend=12.59N
    F-gravity=19.6N
    F-Tens=?
    This is for Mass 2 on the incline

    For mass 1 I got

    F-gravity 9.8
    F-Tens=?

    So I have been trying to use the Ʃ all forces=ma for both equations, this gives me

    M2= ƩF=ma=Ftens-Ffrict+Fparallel
    ƩF=2kg*a=Ftens+(-.15*12.59N)+15.01N

    M1=ƩF=ma=Ftens-Fgrav
    ƩF=1kg*a=Ftens-1N

    Then I put the above M1 equation into M2 and solve for acceleration then plugging in a into either equation to get Ftens. I already know the answer a=-.183 I just want to beat on my craft so when the test rolls around I can set up quick variable templates then plug and chug. Areas of doubt are,

    -signs
    -what to do about friction in the sum I already know its going anticlockwise so Friction is negative correct?
    -Plugged it in many times and cannot get the known answer.

    Thanks for any help and I will keep this post updated if I come across the answer before I receive help
     
  2. jcsd
  3. Oct 3, 2013 #2
    one mistake the friction coefficient is multiplied to F parallel
     
  4. Oct 3, 2013 #3
    for my final equation I get a= -m2g-Ffriction+Fparallel/Mass1+Mass2

    Help
     
  5. Oct 3, 2013 #4
    figured it out. Complete waste of time on here... Get an infraction quickly but no response.
     
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