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Homework Help: Inclined plane with friction, find kinetic energy.

  1. Nov 19, 2011 #1
    I need someone to double check it, because this was an exam given by my teacher and I am trying to solve it, but I do not have any results so I would like to know if I did it correctly or not. Thank you!

    1. The problem statement, all variables and given/known data

    Two blocks m1 = 50kg and m2= 100kg are attached to a rope as shown in figure. Pulley is massless. The angle of the inclined plane is pi/6 and the coefficient of kinetic friction is 0.250. Find the variation of kinetic energy if the body m1 goes up 20meters.


    2. Relevant equations
    F = ma
    kinetic energy = 1/2 mv^2
    kinetic friction = mu*normal force.

    3. The attempt at a solution
    See attachment
    or: http://i40.tinypic.com/6hklm8.jpg for better quality.

    Thanks for any help.
     

    Attached Files:

  2. jcsd
  3. Nov 19, 2011 #2

    Delphi51

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    Welcome to PF! Thanks for taking time to show your whole solution so clearly.

    Over on the right side, where you first have "a =", it appears you are missing a "-m₂g" in the numerator. Also, the "μ*m₁*cos(30)" should have a factor of g as well. I end up with a negative acceleration (m₂ goes down) of about 4.
     
  4. Nov 19, 2011 #3
    Aw, how could I fall in such a stupid typos mistakes ! :(.
    Thanks a lot, that's appreciated. Forgetting about the "numbers" is the reasoning correct ( I mean the use of the formulas) or is there anything wrong? Thanks a lot!
     
  5. Nov 19, 2011 #4

    Delphi51

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    Yes, it all looks good! Nice use of variables right up to the calculation stage.
     
  6. Nov 19, 2011 #5
    Alright! Thanks a lot, I am grateful and I appreciate your help. Thanks again :)
     
  7. Nov 19, 2011 #6

    Delphi51

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    Homework Helper

    Most welcome.
     
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