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Friction/energy help

  1. Oct 6, 2009 #1
    1. The problem statement, all variables and given/known data
    A 3.00 kg mass, m1, slides up a ramp. The angle for the ramp is 28*. The 3.00 kg mass is connected to a second mass, m2, of 3.25 kg by a light string with a frictionless pulley. Coeeficient of kinetic friction is 0.285. Find the acceleration of m1, the kinetic energy of m1 after it has traveled 25 cm up the ramp, and the work done on m1 to moce it the 25 cm.

    2. Relevant equations
    Fr = μN
    EK = (1/2)mv^2
    Besides this I don't know

    3. The attempt at a solution
    Well the friction would be .285 times the normal force of m1, which I think is 26.49. So I got the force of friction is 7.55 N. Then I subtracted 7.55 from 9.81, the acceleration on m2. But I don't think any of this is right. Help?
     
  2. jcsd
  3. Oct 6, 2009 #2

    Delphi51

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    Homework Helper

    Your normal force looks okay, though I got the slightly different 26.0 N.
    In the ramp problem, you really have to have a diagram like this:
    ramp.jpg
    The mg force down needs to be separated into a part perpendicular to the ramp (N) and a part parallel to the ramp. Then you forget all about the mg and just use the components. So far two forces on the 3 kg mass - the friction and the parallel part of gravity. You also have the the tension on the string. Write that the sum of those forces is equal to ma.

    The location of the 2nd mass is unclear. But you'll need another F = ma equation for that. With two equations you should be able to eliminate the Tension and find the acceleration. Please show your work so it is easy to tell how you got answers.
     
  4. Oct 6, 2009 #3
    Last edited by a moderator: May 4, 2017
  5. Oct 6, 2009 #4

    Delphi51

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    Nice job! The free body diagram and F = ma for the second mass should be easy.
     
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