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Physics

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a stone is dropped from a 75m building. when a stone has dropped 15m, a second stone was thrown downward with an initial velocity such that the two stones hit the ground at the same time. what was the initial velocity of the second stone.

  • Physics - ,

    d = Vo*t + 4.9t^2 = 15,
    0 + 4.9t^2 = 15,
    t^2 = 3.06,
    t = 1.75s. = Time to fall 15m.
    Therefore, the 1st stone had a 1.75s
    headstart:

    d1 = 0 + 4.9t^2 = 75
    t^2 = 15.31,
    t1 = 3.91s.

    t2 = 3.91 - 1.75 = 2.16s.
    d2 = Vo*t + 4.9t^2 = 75,
    2.16*Vo + 4.9(2.16)^2 = 75,
    2.16Vo + 22.9 = 75,
    2.16*Vo = 75 - 22.9 = 52.1,
    Vo = 24.1m/s. = Initial velocity of 2nd stone

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