Question

Disregarding air resistance, what is the speed of a ball dropped from 12 feet just before it hits the ground? (Use 1 ft = 0.30 m, and use g = 9.8 m/s2.)

2.4 m/s
8.4 m/s
10.8 m/s
15.3 m/s

Answer 1

Use v^2 = v0^2 + 2gh with v0 = 0 and h = 12 ft = 12(0.30) = 3.6 m:

v = sqrt(2·9.8·3.6) = sqrt(70.56) ≈ 8.4 m/s.

Answer: 8.4 m/s.