The average speed of a train is 24.0km/hr. Suppose a train moving at this speed accelerates - 0.20 m/s^2 until it reaches a speed of 8.0 km/hr. How long does it take the train to undergo this change in speed?

time = 2.2 sec

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