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Homework Help: Can anybody check if I solved this correctly?(tension forces + pulley)

  1. Oct 19, 2013 #1
    1. The problem statement, all variables and given/known data
    The pulley can rotate and has no friction.
    Block [itex]m_2[/itex] is twice as big as [itex]m_1[/itex]
    Find the tensions, [itex]T_1, T_2, T_3[/itex]

    2. Relevant equations
    Newton's second law

    3. The attempt at a solution
    Tension 1:
    By creating a free body diagram only for the block, I got with Newton's second law:

    Tension 2:

    Tension 3:

    Inserting above values for the other tensions:

    Did I solve this correctly? What about the acceleration? Can I do anything about that?
    Last edited: Oct 19, 2013
  2. jcsd
  3. Oct 19, 2013 #2

    the pulley has no net force acting on it.
  4. Oct 19, 2013 #3
    What exactly do you mean?
    Are the 2 first tensions correct?
  5. Oct 19, 2013 #4
    So we have:



    Since the tension is uniform on the string:

    Substituting this into the first equation:

    The tension of the pulley since it has no net force acting:

    Since [itex]T_1=T_2=T[/itex]

    Inserting the tensions:
    Last edited: Oct 19, 2013
  6. Oct 20, 2013 #5


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    Assuming the pulley has no moment of inertia, that all looks correct. I wouldn't write the final answer as [itex]T_3=2\frac{4}{3}mg[/itex] though. It looks like you mean "two and four thirds".
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