A train moves on a straight track in three successive phases.
Phase I: It accelerates uniformly from 10m/s to 25m/s in 30s.
Phase II: It then maintains the speed of 25m/s for 120s (uniform motion, no acceleration).
Phase III: Finally, it decelerates uniformly to 5m/s in 15s.
Answer the following questions.
(i) Calculate the acceleration during Phase I.
(ii) Determine the speed of the train 12s after the start of Phase I.
(iii) Compute the magnitude of the retardation during Phase III.
(iv) Taking the forward direction as positive, describe the sign of acceleration in each phase and justify your answer briefly.