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Torque and angular acceleration of two discs

  1. Apr 24, 2013 #1
    1. The problem statement, all variables and given/known data


    2. Relevant equations

    Ʃ[itex]\tau[/itex] = I[itex]\alpha[/itex]
    ƩF = ma

    3. The attempt at a solution

    I was able to calculate A and B which I am confident is correct..


    for part C is what I'm having trouble with. Since both disks are fixed together, does that mean they share the same angular acceleration? if so I think the way to go about this is I apply the equation

    Ʃ[itex]\tau[/itex] = I[itex]\alpha[/itex]

    where it will be T1R1 - T2R2 = I[itex]\alpha[/itex] and I just solve for alpha.

    but since they are now accelerating.. doesn't that change each tension to be t = mg + ma? instead of just t = mg ? which then makes it much more difficult to solve..

    unless if the tensions are just mg then it will be fairly easy to solve since I can find the alpha of the rotating system then just apply the equation

    a = [itex]\alpha[/itex]R

    and calculate the a for each, and from there I will be able to find the tensions in each rope.
  2. jcsd
  3. Apr 24, 2013 #2

    Simon Bridge

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    Yes - that is what "fixed together" means. You needed to assume this to do (a) and (b).

    Use the free-body diagram to inform you of the tensions. Don't anticipate.
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