Recall the definition of average velocity:
average v = ∆x / ∆t
The driver moves a distance of ∆x = 4.25 km = 4250 m in 2 min = 120 s, so the average velocity is
average v = (4250 m) / (120 s) ≈ 35.4 m/s
Under constant acceleration, the average velocity can also be computed by taking the average of the initial and final velocities:
average v = (initial v + final v) / 2
Solve for (final v) :
35.4 m/s = (20 m/s + final v)/2
final v ≈ 50.83 m/s
Recall the definition of average acceleration:
average a = ∆v / ∆t
Solve for a :
a = (50.83 m/s - 20 m/s) / (120 s)
a ≈ 0.257 m/s²