After a stone dropped from a cliff has fallen 20 m, the stone's speed is approximately
A) 10 m/s.
B) 20 m/s.
C) 196 m/s.
D) 392 m/s.

Question

Quizplus · Accepted Answer

The speed of a falling object increases due to gravity. The acceleration due to gravity near the surface of the Earth is approximately 9.8 m/s².

Using the kinematic equation, vf² = vi² + 2ad, where vf is final velocity, vi is initial velocity (usually 0 m/s), a is acceleration, and d is distance, we can find the final velocity of the stone when it has fallen 20 meters:

vf² = 0 + 2(9.8 m/s²)(20 m)
vf = 19.8 m/s

Therefore, the stone's speed is approximately 20 m/s (rounded to the nearest whole number), which is answer choice B.

After a Stone Dropped from a Cliff Has Fallen 20