Acceleration is defined as the rate of change of velocity (dv/dt). Thus, the change is velocity is equal to the acceleration. In this question, the acceleration of the vehicle (moving in a straight line) is given as 2 km/h.s. Thus, the speed of the vehicle changes by 2 km/h every second. Since the vehicle is moving in the straight line, speed and velocity are the same. We can also convert this change in speed in meters per second, by using the knowledge that a km consists of 1000 meters and an hour can be divided into 3600 seconds.
Thus 2 km/h = 2 x (1000 m)/(3600 sec) = 2000/3600 m/sec = 0.56 m/sec
Thus, the speed of the vehicle changes by 2 km per hour or 0.5 meters per second every second of its motion.
Hope this helps.