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Torque and Inertia of objects on Inclined plane

  1. Mar 24, 2008 #1
    1. The problem statement, all variables and given/known data
    a block with mass m1= 2 kg, and a block of mass m2 = 6kg are connected by a massless string over a pulley in the shape of a solid disk having radius R = .25m and mass M = 10 kg. These blocks are allowed to move on a fixed wedge of angle pheta = 30 degrees. the coefficent of kinetic friction is .36 for both blocks and pulley. Determine A) the acceleration of the two blocks and B) the tensions in the string on both sides of the pulley.


    2. Relevant equations
    well, I already solved part A) I just need help with part B. I used the sumTorque = Ialpha, where alpha = a/R. along with this equation below:


    3. The attempt at a solution
    well, i wanted to solve for a so i did the following:(note f=coefficent of friction*): -T1Rf+60cos(T2)Rf = 1/2mR^2*(a/R) ====> -T1f +60cos(T2)f = 1/2ma.

    M2gf - T1f + 60cosT2f = 1/2Ma
    M2gf = M1af + 60cosM2af + 1/2Ma
    M2gf = a(M1f + 60cosM2f + 1/2M)
    a = M2gf/(M1f + 60cosM2f + 1/2M) = .31 m/s^2

    Im not sure how to solve for the Tension though, do i use the same equation??
     
  2. jcsd
  3. Mar 24, 2008 #2
    The answer for B is 7.67 N and 9.22 N.

    But I want to know how they got that. Can anybody help please?
     
  4. Mar 24, 2008 #3
    can anybody help? do I need to explain more?
     
  5. Mar 24, 2008 #4

    Doc Al

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    Staff: Mentor

    A diagram would be helpful. Are both sides of the wedge at an angle of 30 degrees with the horizontal?

    In any case, assuming you've correctly found the acceleration, just apply Newton's 2nd law to each block separately to find the tensions.
     
  6. Mar 24, 2008 #5
    Im not sure how to put a diagram on this forum, but If i apply newtons second law, I dont end up with the same Tensions as the book answer.

    F = ma
    I come up with 6.08 N for T1
     
  7. Mar 24, 2008 #6

    Doc Al

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    Staff: Mentor

    Show exactly what you did to get the tension. (Until I understand the setup better, I cannot verify your answer for the acceleration.)
     
  8. Mar 24, 2008 #7
    how do I insert an image so i can show you the picture?
     
  9. Mar 24, 2008 #8

    Doc Al

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    Staff: Mentor

    One of the icons in the post editing window is for inserting images. Or you can attach a file.
     
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