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March 30, 2017

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A rock is dropped. How fast will the 5.0 kg rock be traveling in 4.0s if a 5.o N force of air resistance acts on it?

  • physics - ,

    In the real world, the air resistance will not be constant as it falls. It will be proportiuonal to the square of velocity.

    Assume that 5 N is the AVERAGE friction force during the 4 seconds. There is also a weight force of M g = 49 N pushing it down. The net average force in the downward direction is 44 N.

    Impulse = 44 N * 4s = Momentum gain
    = M*Vfinal

    Vfinal = 44*4 /M = 35.2 m/s

    Without friction, Vfinal would be
    g*t = 9.8 * 4 = 39.2 m/s

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