It takes 20 seconds for a train to travel at a constant speed through a 450m long tunnel. There is a lamp on the tunnel, and the light shines on the train for 5S Find: (1) the length of the train; (2) The time when the train is completely in the tunnel There is a lamp in the tunnel. The time when the light shines on the train is 5S. What do you mean ////////

It takes 20 seconds for a train to travel at a constant speed through a 450m long tunnel. There is a lamp on the tunnel, and the light shines on the train for 5S Find: (1) the length of the train; (2) The time when the train is completely in the tunnel There is a lamp in the tunnel. The time when the light shines on the train is 5S. What do you mean ////////

Set the unknown number, the train length is x, the speed is Y M / s, x + 450 = 20Y, 5Y = x (1) x = 150m, y = 30m / s
(2)(450-150)/30=10
The train is 150m long and runs for 10s
There is a light in the tunnel. The time when the light shines on the train is 5S, which means that the train passes from the front to the rear. This light takes 5S, so the speed x5s = the length of the train

It takes 20 s for a train to pass through a 450m tunnel. There is a lamp on the tunnel, which shines vertically downward. The time on the train is 5 s 1 find the length of the train 2 find the time when the train runs completely in the tunnel Question 2, remember it's time to drive completely in the tunnel * * * * * * * *

Train length 150m
It takes 10 seconds to drive completely in the tunnel
Set the vehicle length as X and the speed as YM / s
（x+450）/y=20
X = 150, y = 30
The length of the train running completely in the cave needs to subtract its own length, so
（450-150）/30=10

It takes 20 seconds for a train to travel at a constant speed through a 450m long tunnel. There is a lamp on the top of the tunnel, which emits light vertically downward, and the light shines on the train for 5S. According to the above data, calculate: (1) The length of the train; (2) The time when the train is completely in the tunnel

(1) Let the length of the train be x meters,
Equation from the meaning of the question: 450 + X
20=x
5，
Solution: x = 150;
（2）450+150
20=30（m/s），
∴（450-150）÷30=10（s），
Therefore, the length of the train is 150 meters; The time for the train body to be completely in the tunnel is 10 seconds

A 450m long train passed a 1050m long bridge in minutes and seconds, and then passed a tunnel in 40 seconds at the same speed. How long is the tunnel

What are your minutes and seconds? Supplement: 450 + 1050 = x * 80 find out the speed x = how much, and then the tunnel length y + 450 = 40 * x can find y = 300 meters

When introducing the stone arch bridge in China, the order of introducing the structure of the bridge is from - to -

General special summary specific overall local time
I've just done the problem in the Chinese exercise book

Why does the train slow down in advance when passing the bridge

1、 If the speed is high, the number of cars on the bridge will be large at a certain time, and the bearing capacity of the bridge is equal to the sum of the gravity of each car
2、 To avoid resonance