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    Particles A and B, of mass 2m and m respectively, are attached to the ends of a light inextensible string. The string passes over a smooth pulley fixed at the edge of a rough horizontal table. Particle A is held on the table, while B rests on a smooth plane inclined at 30 degrees to the horizontal.
    The particle A is released from rest and begings to move.

    What is the equation of motion of A and B, when the system is released from rest?


    A's fine, just having a bit of trouble with finding B.
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    The particles will have the same acceleration?
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    I know. But could you give me the equations of motion?

    I need to know about the sin's and cos's.

    Adam
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    Let T be the tension in the string

    Mass A is on a rough table, so has a coefft of friction µ.

    Mass B in on a smooth pane, so no friction and force down the plane is mg.sin30°.

    Mass A
    Fr = µ.2mg
    T - Fr = m.a
    T - µ.2mg = 2m.a
    ===========

    Mass B
    mg.sin30° - T = m.a
    ½mg - T = m.a
    =========

    Adding these eqns together,

    ½mg - µ.2mg = 3m.a
    3a = ½g - 2µg
    a = g(1 - 4µ)/6
    =========
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    Cheers. Big help mate.

    Adam
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    (Original post by Fermat)
    Mass B
    mg.sin30° - T = m.a
    ½mg - T = m.a
    =========
    I thought it would be cos? Why isn't it?
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    :confused:
    (Original post by adk)
    I thought it would be cos? Why isn't it?
    why do you think itd be cos? :confused:
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    When you resolve the forces on the block due to its weight, the normal reaction is mg.cosø and the force down the plane is mg.sinø.
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