The equations of motion of a man are "y(t) = h - \\frac{g t^2}{2}" and "v(t) = gt", where "h" is the height of the cliff, "g = 9.81 \\frac{m}{s^2}"- gravitational acceleration. Equating "y(t)" to zero, and solving for "t", obtain "0 = h - \\frac{g t^2}{2} \\Rightarrow t = \\sqrt{\\frac{2 h}{g}}" - this is the time it takes to fall down. Calculating speed at that moment, obtain "v = g \\sqrt{\\frac{2 h}{g}} = \\sqrt{2 g h}".
Calculating for "h = 9 m", obtain "t \\approx 1.35 s", "v \\approx 13.29 \\frac{m}{s}".
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