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Friction and gravity

  1. Oct 29, 2015 #1
    1. The problem statement, all variables and given/known data

    Two blocs with the same mass have the same rope which links them. The friction coefficients are the same whatever the surface. The blocs are initialy stationary and we let them move. What is the module of the acceleration of the blocs if static coefficient of friction =0,25
    Cinetic coefficient of friction = 0,2
    2. Relevant equations

    Newton's second law. Sum forces = ma
    and
    fs or c = u* n (friction formula)
    3. The attempt at a solution
    I don't know what to do to be honest. I know what forces we have, I know how to write Newton's formula for each object and I get a total of 4 formulas for NEwton's second law. But after that, where do I go ?
     
  2. jcsd
  3. Oct 29, 2015 #2

    mfb

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    Staff: Mentor

    Where are the blocks? Why should they move at all? There is something missing.
    They are connected by a rope, so their distance cannot increase.
     
  4. Oct 29, 2015 #3
    I'm REALLY sorry, I forgot this : http://imgur.com/Dw7XvAE
     
  5. Oct 29, 2015 #4

    mfb

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    You should get as many equations as unknowns, so you can solve the problem.
     
  6. Oct 29, 2015 #5
    Ok, so how many ? 2 in 2 ?
     
  7. Oct 29, 2015 #6
    Draw a free body diagram for both blocks and match all the forces acting on the y and x axis
     
  8. Oct 29, 2015 #7

    mfb

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    Staff: Mentor

    That depends on how you set up the equations. Some constraints can be included directly in the choice of variables.
    It would help to show your equations.
     
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