It takes 5 seconds for a train to pass a road sign, 20 seconds to pass a 300 meter long bridge, and how many seconds to cross an 800 meter long cave Write the analysis, too

Assuming that the length of the train is l and the speed is V1, the length of the train can be calculated according to the time of passing the landmark: l = 5v2. According to the time from the front to the rear when passing the 300m bridge, the actual driving distance is 300 + L meters, which takes 20 seconds, we can get: 300 + L = 20V. According to the above combination, we can get v = 20m / s, l = 100m 3

RELATED INFORMATIONS

1. It takes 3.5 seconds for a train to pass a road sign and 20 seconds to pass a 300 meter long bridge. It takes a long time for a train to cross an 800 meter long cave______ Seconds
2. A subway train starts from a static station and moves along a straight line. It first accelerates uniformly with the acceleration A1, and then decelerates uniformly with the acceleration A2 A subway train starts from a static station and moves along a straight line. First, it accelerates uniformly with the acceleration A1, and then decelerates uniformly with the acceleration A2. When it arrives at the station B, it just stops. If the distance between the two stations is x, what is the maximum speed of the train in operation?
3. A subway train starts from a station at rest and moves along a straight line. First, it accelerates uniformly with the acceleration A1, then decelerates uniformly with the acceleration A2. When it arrives at station B, it just stops. If the distance between the two stations is x, find the time t
4. From the station there is a static train out of the uniform acceleration movement, the first 1 min running 540 m to calculate acceleration~
5. The train starts from ground a at rest and accelerates to ground B at a constant acceleration of a, then decelerates to ground C at a constant acceleration of a / 3 in the original direction and stops If the distance between a and C is 28.8km, the vehicle has been running for 24min
6. The train goes from ground a to ground B with constant acceleration a, and then decelerates to ground C with constant acceleration a / 3 in the original direction. The distance between ground a and ground C is 18km, and the train runs for 20min. The distance between ground a and ground B and the acceleration a are calculated
7. The train starts from station a and makes a uniform acceleration with acceleration of A. after passing station B, it changes to drive along the original direction and decelerates with acceleration of a, and stops at station C. It is known that the distance between station a and station C is 24km, and the train has been running for 24min, then the distance between station a and station B is 24km____ Km, the speed of the train passing station B is____ km / min . The answer is 6 and 2 Sorry, the second a should be changed to a / 3, I didn't notice when I was fighting
8. First, do the uniform acceleration motion with the acceleration of A1, and then do the uniform deceleration motion with the acceleration of A2 According to the meaning of this sentence, A1 × t = A2 × t ', instead of adding a negative sign before A2, right?
9. A train starts at a standstill and moves in a straight line with a constant acceleration of a = 0.5 m / S2. We can find: (1) what is the speed of the train at the end of the third second? (2) What is the average speed in the first four seconds? (3) What is the displacement in the second 4S?
10. A train starts to move in a straight line with uniform acceleration at an acceleration of 0.5m/s from standstill (1) What's the speed of the train at the end of the fourth second? (2) What is the average speed in the first three seconds? (3) What is the displacement at 5S? (4) What is the displacement in the second 5S?
11. It takes 5 seconds for a train to pass a road sign, 20 seconds to pass a 300 meter cave, and how many seconds to pass an 800 meter bridge? Using equation
12. It takes 6.5 seconds for a train to pass a sign, 23 seconds to pass a 300 meter long bridge, and a few seconds to cross an 800 meter long cave
13. It takes 3.5 seconds for a train to pass a road sign and 20 seconds to pass a 300 meter long bridge. It takes a long time for a train to cross an 800 meter long cave______ Seconds
14. The temperature of the track rises when the train is running on it The teacher said that this is the same as the friction between hands, overcoming the friction to do work I mainly want to understand why the temperature of the rail rises because of work Can it be understood as follows: When the train is running, it overcomes the friction to do work, and the internal energy increases and the temperature rises; Because the friction is mutual, the rail is also subject to friction. If the train is taken as a reference, the rail is moving and works against the friction Is that right?
15. The speed of a train is 10.8km/h when it passes a road sign, and it becomes 54km / h after 1min, How long will it take for the train to reach 72 km / h?
16. The train Accelerates along the straight track at a speed of 10.8km/h after passing a road sign
17. The train Accelerates along the straight track at a speed of 10.8 km / h when passing a landmark
18. The speed of the train is 10.8km/h when it passes a road sign, and 54km / h after 1min. How long does it take for the train to reach 64.8km/h?
19. When a plane takes off and taxis, it starts to make uniform acceleration linear motion from static state, with the acceleration of 4m / S2. When the taxiing speed of the plane reaches 85m / s, it leaves the ground and takes off. If the plane suddenly receives the command from the command tower to stop taking off when it reaches the take-off speed, the pilot immediately stops the plane, and the plane makes uniform deceleration linear motion, with the acceleration of 5m / S2 How long does it take for a plane to reach maximum speed from take-off? (2) How long does the plane take from take-off to stop?
20. Recursively seeking the first 30 items of sequence 1 1 3 5 9 17 31 57