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Homework Help: Friction - minimum value of force for movement

  1. Jun 21, 2014 #1
    1. The problem statement, all variables and given/known data

    Determine the minimum value of the force F for which the systems start moving. Assume M1 = 1kg, M2 = 2kg, Us = 0.3.
    Solution: F = 9; F = 6N

    My problem is that i dont know the forces acting on wheel.

    2. Relevant equations

    3. The attempt at a solution
    M1 :
    F - T = 0
    M1g - N = 0
    Fr - T = 0
    M1g+M2g - N(from mass 1 and mass 2) = 0
  2. jcsd
  3. Jun 21, 2014 #2


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    Hello voliseq. Welcome to PF !

    Which wheel (or wheels) ?
  4. Jun 21, 2014 #3
    Hi Sammy, i mean those wheels attached to M1 (on first picture) and M2(on second picture).
  5. Jun 21, 2014 #4
    The only forces acting on the wheels are normal (vertical) forces. The wheels are free to rotate, so the horizontal forces acting on them are zero.

  6. Jun 22, 2014 #5
    Another problem

    Thanks Chest it works, now i have got another problem to solve,
    1. Here is the problem


    2. And here is my attempt at solution


    I think something is wrong here as i cant get correct result
  7. Jun 22, 2014 #6
    The members AB and BC need to be in equilibrium. In terms of P, what is the normal force exerted by the cylinder on AB? What is the normal force exerted by AB on the cylinder?

  8. Jun 22, 2014 #7
    N = Pcos30 ?
  9. Jun 22, 2014 #8
    Please try again, taking moments about the pin.

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