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M1 problems with pulleys question. watch

    • Thread Starter

    Can someone please help with this question.

    P= 3kg, Q=6kg

    P and Q are attached to the ends of a light inextensible string. String passes over smooth fixed pulley. System released from rest, both masses 2m above horizontal floor. A) Find how long it takes for particle Q to hit floor. B) Assuming P does not reach the pulley, find its greatest height above floor.

    I've done A)

    3g=9a so, 29.4=9a so, a=3.27

    using s=ut+1/2at^2


    But how do I work out B) the greatest height?

    you know how high above the floor P is when Q hits the floor ( how far has Q moved down,.... they are attached!) But when Q hit the floor, P has a velocity and will keep on moving upwards, (the string goes slack) think what force is acting on P now, and what do you know about the velocity of P at the greatest height.
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Updated: March 18, 2009

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