11 October, 16:12
A rock dropped from a 20 meter bridge falls into the river below. How long did it take to reach the water? What velocity did it hit the water with.
11 October, 18:00
2 s, - 20 m/s
y₀ = 20 m
y = 0 m
v₀ = 0 m/s
a = - 9.8 m/s²
Find: t and v
y = y₀ + v₀ t + ½ at²
0 = 20 + 0 + ½ (-9.8) t²
0 = 20 - 4.9 t²
t ≈ 2 s
v² = v₀² + 2a (y - y₀)
v² = 0 + 2 (-9.8) (0 - 20)
v ≈ ±20 m/s
Since the rock is falling, v = - 20 m/s.
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» A rock dropped from a 20 meter bridge falls into the river below. How long did it take to reach the water? What velocity did it hit the water with.