If your car accelerates from rest at a steady rate of 4 m/s2, how soon will it reach 84 km/h

Answer 1

V = 81km/h = 81000m/3600s = 22.5 m/s.

V = Vo + at = 22.5 m/s.
0 + 4*t = 22.5
t = 5.625 s.