Constant velocity/acceleration

Question

A car accelerates from the rest until it is traveling at 88km/hr for 6.2seconds. The time to keep up to speed is 6.2 seconds. What is the acceleration of the car in m/s2? How far did the car travel in 6.2 seconds in meters?

Answer 1

We are give km/hr but want answers in m/s. Convert 88 km/hr to m/s as follows:

88 km/hr * (1000 m / 1 Km) * (1 hr / 3600 sec) = 24.444 m/s

a) Acceleration is by definition change in speed divided by time: a = (24.444 - 0) / 6.2 = 3.943 m/s²

b) When the acceleration is constant, when can use average speed to get the answer. In this case, the average speed is (0 + 24.444) / 2 = 12.222 m/s. The distance travelled is just speed*time:

d = 12.222 m/s * 6.2 s = 75.776 m

The problem give quantities to 2 significant figure, so the answers to this problem are:

a) 24 m/s²

b) 76 m