Since the train is moving at a constant velocity, we can assume that there is no static friction involved between the wheels of the train and the rail. This also means that there is no acceleration happening. Thus, the force of gravity acting on the train has been overcame by the strength of the engine going to the east. Another force that was also overcame was the resistant force of the air during impact to the head of the train. Hence, the train is constantly moving without accelerating.
