15. A train travelling along a straight track starts from rest at point A and accelerates uniformly to 20 m s' in 20 s. It travels at this speed for 60 s, then slows down uniformly to rest in 40 s at point C. It stays at rest at C for 30 s, then reverses direction, accelerating uniformly to 10 min 10 s. It travels at this speed for 30 s, then slows down uniformly to rest in 10s when it reaches point B. Plot a graph of the motion of the train. b Use your graph to calculate
i the train's displacement from point A when it reaches a point C
ii the train's displacement from point A when it reaches point B
iii the train's acceleration each time its speed changes.