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physics

Two objects (39.0 and 21.0 kg) are connected by a massless string that passes over a massless, frictionless pulley. The pulley hangs from the ceiling. Find (a) the acceleration of the objects and (b) the tension in the string.

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  1. total mass accelerated = 39+21 = 60 kg
    total force accelerating = (39-21)g = 18*9.81 = 177 N
    a = F/m = 177/60 = 2.95 m/s^2

    total force up on little mass = 21 * acceleration up

    T - 21(9.81) = 21(2.95)
    T = 21 (12.76) = 268 N

    check
    total force down on big mass = 39*.34 ??
    39*9.81 - T = 39(2.95)?
    383 - 268 = 115 ?? Yes, good

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