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A rock is thrown vertically upward with a speed of 14.0 m/s from the roof of a building that is 50.0 m above the ground. Assume free fall.

In how many seconds after being thrown does the rock strike the ground? in s

What is the speed of the rock just before it strikes the ground? in m/s

  • physics -

    Vf^2 = Vo^2 + 2gd,
    d = 50 + (Vf^2 - Vo^2) / 2g,
    d = 50 + (0 - (14)^2) / -19.6,
    d = 50 + 10 = 60m above ground.

    Vf = Vo + gt,
    t(up) = (Vf - Vo) / a,
    t(up) = (0 - 14) / -9.8 = 1.43s.

    d = Vo*t + 0.5gt^2 = 60m.
    0 + 0.5*9.8t^2 = 60,
    4.9t^2 = 60,
    t^2 = 12.24,
    t(down) = 3.50s.

    T = t(up) + t(down),
    T = 1.43 + 3.50 = 4.93s

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