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Static friction

  1. Oct 14, 2009 #1
    1. The problem statement, all variables and given/known data

    a mass m is supported as shown in the figure by ideal strings connected to a rigid wall and to tal mass 3m sitting on a horizontal surface. what is the minimum coefficient of static friction between the larger mass and the surface that permits the system to remain in equilibrium in the situation shown

    2. Relevant equations



    3. The attempt at a solution

    Big block

    Fx = u3mg - T = 0

    Little block & strongs

    Fx = T - mgsin60 = 0

    T = us3mg - mgsin60


    I dont think this is correct. How do u deal with the string intersection
     

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  3. Oct 14, 2009 #2

    rl.bhat

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    For big block Fx = μ*3mg - T*sin30 = 0
    For smaller block Fy = .....?
     
  4. Oct 15, 2009 #3
    Why is the tension have the sin 30 doesnt the tension come directly in the x plain

    so is Fy = mg - Tcos30 = 0
     
  5. Oct 15, 2009 #4

    rl.bhat

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    Correct.
    Eliminate T and find the value of μ.
     
  6. Oct 15, 2009 #5
    u3mg -Tsin30 = 0
    mg - t cos30 = 0 t = mg/cos30
    u3mg - mgsin30(cos30) = 0
    u = tan30/3
     
  7. Oct 15, 2009 #6

    rl.bhat

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    Correct.
     
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