A girl drops a pebble from rest off a high cliff. It falls for 2.00 s before hitting the water below. Using g = 9.80 m/s^2, how fast is the pebble going when it hits the water?
A9.80 m/s
B10.0 m/s
C19.6 m/s
D20.0 m/s
Answer & Solution
Correct answer: C. 19.6 m/s
1. Dropped from rest means v_0 = 0.
2. v = v_0 + gt = 0 + (9.80 m/s^2)(2.00 s).
3. v = 19.6 m/s.
_Source: OpenStax Physics (CC BY 4.0), Ch 3 "Acceleration", section 3.2 Representing Acceleration with Equations and Graphs_
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