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Math Help - Mechanics help, resolving forces

  1. #1
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    Mechanics help, resolving forces

    Two particles P and Q of equal mass are connected by a light inextensible string. The string passes over a small smooth pulley which is fixed at the top of a fixed wedge. One face of the wedge is smooth and inclined to the horizontal at an angle of 30° and the other face of the wedge is rough and inclined to the horizontal at an angle of 60°. Particle P lies on the rough face and particle Q lies on the smooth face with the string connecting them taut. The coefficient of friction between P and the rough face is 0.5.
    a Find the acceleration of the system.
    b Find the tension in the string.


    for Q resolving vertically : T-mgcos60 = ma

    for P, resolving horizontal : S = mgcos60

    and resolving vertically for P : mg- t + mgcos30 = ma

    mg = 2s

    is this so far correct? Am not sure if these equation are correct, or what to do next?

    Any help appreciated.

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  2. #2
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    Re: Mechanics help, resolving forces

    forces acting on Q parallel to its incline ...

    T - mg\sin(30) = ma

    forces acting on P parallel to its incline ...

    mg\sin(60) - T - \mu mg\cos(60) = ma

    sum the two equations ...

    mg\sin(60) - mg\sin(30) - \mu mg\cos(60) = 2ma

    \frac{g\sin(60) - g\sin(30) - \mu g\cos(60)}{2} = a

    calculate a , then go back to either starting equation and calculate the tension force
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