time = 2.2 sec
Step-by-step explanation:
The initial speed of train = 24 km/hr = 24 x 1000/3600 = 20/3 m/sec
The final speed of train = 8 km/hr = 8 x 1000/3600 = 20/9 m/sec
The relation of motion
v = u + a x t
final velocity = initial velocity + acceleration x time
20/9 = 20/3 - 2 x t where t is time
Because the acceleration is negative
2 t = 20/3 - 20/9 = 40/9 or t = 20/9 sec = 2.2 sec
The time taken to decrease the speed from 24 km/hr to 8 km/hr is 2.2 sec approx