hs 2. A commuter train travels between two downtown stations. Because the stations are only x=1000 m apart, the train never reaches its maximum possible cruising speed. During rush hour the engineer minimizes the travel interval At between the two stations by accelerating for a time interval At, at a1 = 0.100 m/s2 and then immediately braking with acceleration a2 = 0.500 m/s2 for a time interval Atz. (a) Derive the expression to determine At; note that At, and Atz are not given (8 points) (b) Calculate At (2 points)