Answer:
a) 17.49 seconds
b) 13.12 seconds
c) 2.99 m/s²
Step-by-step explanation:
a) Acceleration = a = 1.35 m/s²
Final velocity = v = 85 km/h =

Initial velocity = u = 0
Equation of motion

Time taken to accelerate to top speed is 17.49 seconds.
b) Acceleration = a = -1.8 m/s²
Initial velocity = u = 23.61\ m/s
Final velocity = v = 0

Time taken to stop the train from top speed is 13.12 seconds
c) Initial velocity = u = 23.61 m/s
Time taken = t = 7.9 s
Final velocity = v = 0

Emergency acceleration is 2.99 m/s² (magnitude)