A train is travelling down a straight track at 20m/s when the engineer applies the brakes,resulting in an acceleration of -1.0m/s^2 as long as the train is in motion. How far does the train move during 40-s time interval starting at the instant the brakes are applied? After 40s, displacement become zero,but the given answer is 200m. So, does it mean the 40s is just to confuse us? Does this question mean the train stop deceleration after it reach zero final velocity? Thanks.