A car starts from rest and accelerates at 3.0 m/s^2 for 6.0 s. What is its final velocity?

A car starts from rest and accelerates at 3.0 m/s^2 for 6.0 s. What is its final velocity?

• A. 12 m/s
• B. 27 m/s
• C. 18 m/s
• D. 21 m/s

Answer: (C)

Under constant acceleration, velocity changes linearly with time: v = v0 + a t. Starting from rest means v0 = 0, so v = a t. With a = 3.0 m/s^2 and t = 6.0 s, the final velocity is v = (3.0)(6.0) = 18 m/s. The units work out as m/s because m/s^2 times s cancels to m/s. If you mixed up the time or added a nonzero initial velocity, you’d get a different number, but with these values the result is 18 m/s.

Under constant acceleration, velocity changes linearly with time: v = v0 + a t. Starting from rest means v0 = 0, so v = a t. With a = 3.0 m/s^2 and t = 6.0 s, the final velocity is v = (3.0)(6.0) = 18 m/s. The units work out as m/s because m/s^2 times s cancels to m/s. If you mixed up the time or added a nonzero initial velocity, you’d get a different number, but with these values the result is 18 m/s.