It takes 20 seconds for the train to pass through a 300-meter-long tunnel. There is a lamp at the top of the tunnel, which shines vertically downward. The time when the lamp shines on the train is 10s. 1. Let the length of the train be x meters, which is expressed by the formula containing x: the distance from the front of the train to the rear of the train under the light and the average speed of the train during this time; 2. Let the length of the train be x meters, which is expressed by the formula containing x: the distance traveled by the train from the front of the tunnel to the rear of the tunnel and the average speed of the train during this time; 3. Has the average speed of the train changed in the appeal? Find out the length of this train.
The answer is as follows:
1, the distance from the front of the train passing under the light to the rear of the train passing under the light =x meters,
The average train speed during this period =X/ 10 m/s.
2. The distance traveled by the train from the front of the train entering the tunnel to the rear of the train leaving the tunnel = x+300.
The average train speed during this period = (x+300)/20m/s.
3. The average speed of the train in the appeal remains unchanged.
4、X/ 10=(X+300)/20
The solution is X=300,
This train is 300 meters long.