An engine is used to pull a train of two cars out of a mine. The floor slopes upward at an angle of 30°. Each car has a mass of 10^4 Kg and normally travels without friction on the tracks. The engine can exert a maximum force of 1.5x10^5 N on car A. If the engineer again throttles back so that the force exerted by the engine on car A decreases at the constant rate of 3 N per second, how long before the train stoprs moving up the track? Assume the original speed was 3 m/s