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Simple newtonian mechanics problem

  1. Jul 17, 2011 #1
    1. The problem statement, all variables and given/known data
    It is the review problem on p.131 of Physics for scientists and engineers ( Serway, 4th edition).
    It is the classical problem of 2 blocks in an incline(with angle [itex]\theta[/itex]) with masses 2m and m (in order from bottom to the top of the incline) and 1 block suspended trough a pulley with mass M.
    He asks to find M and give the answer as function of m, g, [itex]\theta[/itex].

    2. Relevant equations
    I got to 2 equations, they are:
    [itex]Mg =4ma+3mg\cos\theta[/itex]

    and

    [itex]a=\frac{g(M-3m\cos\theta)}{M+3m}[/itex]

    I couldn't get to something that wasn't a form of M2+... and it get very strange.
    Some tip?

    3. The attempt at a solution
    It is above.
     
  2. jcsd
  3. Jul 17, 2011 #2

    gneill

    User Avatar

    Staff: Mentor

    Presumably the blocks on the incline are connected to each other?

    Is there some information in the problem statement regarding the type of motion expected? Otherwise, there doesn't appear to be any constraint on the the mass M.
     
  4. Jul 18, 2011 #3
    Thank you,

    After i read your reply i went back to check the exercise and i noticed that the sistem is in equilibrium !!
    I need to be a little more attentive to the details.
    it is really just a "simple newtonian mechanics problem".
     
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