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.

2 s, - 20 m/s

Explanation:

Given:

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.