Question

A car starts from rest and accelerates uniformly for a five seconds along a straight road. If speed obtained by the car is 72 km/h, then its acceleration is 

Answer 1

By definition, the acceleration is:

$$a = \dfrac{v_f - v_i}{t}$$

where $v_f = 72km/h = 20m/s$ is the final speed, and $v_i = 0$ is the initial speed (start from rest). $t = 5s$ is the time.

Thus, obtain:

$$a = \dfrac{20m/s - 0m/s}{5s} = 4m/s^2$$

Answer. 4 m/s^2.