The distance from the base of the building the rock will land is 26.4 m
h = ½gt²
8.5 = ½ × 9.8 × t²
8.5 = 4.9 × t²
Divide both side by 4.9
t² = 8.5 / 4.9
Take the square root of both side
t = √(8.5 / 4.9)
t = 1.32 s
s = ut
s = 20 × 1.32
s = 26.4 m
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