Two trains

The train runs at speed v1 = 72 km/h. The passenger, sitting in the train, observed that a train long l = 75m in 3 s passed on the other track in the opposite direction. Calculate the speed of this train.

Correct answer:

v₂ =  18 km/h

Step-by-step explanation:

$$\begin{gathered} v_1=72\text{ km/h}\to \text{ m/s}=72\mathrm{/}3.6\text{ m/s}=20\text{ m/s } \\ l=75\text{ m } \\ t=3\text{ s } \\ t={\displaystyle \frac{l}{v_1+v_2}} \\ {v}_1\cdot t+v_2\cdot t=l \\ {v}_{22}={\displaystyle \frac{l-v_1\cdot t}{t}}={\displaystyle \frac{75-20\cdot 3}{3}}=5\text{ m/s } \\ {v}_2=v_{22}\to \text{ km/h}=v_{22}\cdot 3.6\text{ km/h}=5\cdot 3.6\text{ km/h}=18\text{ km/h} \end{gathered}$$

Try another example

Related math problems and questions:

• Double-track line
  A 160 m long passenger train runs on a double-track line in one direction at a constant speed of 54 km/h, and a 240 m long express train in the opposite direction. a) How fast is the express train if passing the passenger train driver for 6 s? b) How long
• Two trains
  Through the bridge, long l = 240m, the train passes through the constant speed at time t1 = 21s. A train running along the traffic lights at the edge of the bridge passes the same speed at t2 = 9s. a) What speed v did the train go? b) How long did it take
• Two trains
  From station A, the freight train traveled at a speed of 40 km/h in 9h. When he drove 15km, the fast train started from station A in the same direction at a speed of 70km/h. When will it the freight train catch up?
• The train
  The train passed the observer in the 20s and passed through a 1500m tunnel in 2 minutes. Calculate the speed (km/h) and train length.
• Railroad
  The railroad runs parallel to the railway. The train travels at 36 km/h on track. In the opposite direction, the motorcycle rides at 90 km/h. The train passes in 3 seconds. How long is a train?
• Two trains meet
  From A started at 7:15 express train at speed 85 km/h to B. From B started passenger train at 8:30 in the direction to A and at speed 55 km/h. The distance A and B are 386 1/4 km. At what time and at what distance from B the two trains meet?
• Double-track
  On double-track express met with a freight train. Express travel at speed 72 km/h, a freight train at speed 36 km/h. After what time period will be from 9 km apart?
• Train 2
  The train slowed down from 90 km/h to 72 km/h in 5 seconds. How long track travel?
• Train
  A passenger train traveled for 2 hours 74 km. 3.1 hours after its departure started fast train and caught it on 186 km. How many km/h is different its average speeds?
• Trains
  From station 130 km away started passenger train and after 2.2 hours after the express train, which travels 37 km an hour more. Express train finish journey 7 minutes early. Calculate the average speed of this two trains.
• Truck and car
  At 6h45min, the truck started at a speed of 36 km/h. At 7h30m behind it a passenger car. Find the passenger car's average speed to catch the truck 72 km away from the factory.
• Train speed
  The train speed is decreased during 50 sec from 72 km/h to 36 km/h. Assuming that the train movement is equally slowing, find the the acceleration and the distance that it travels at.
• Trains for people
  It is said that the train is synonymous to delay. Calculate the average speed of travel by train long 85 km, with regular train leave at 7:00 and arrive at 8:18, but train is late and has departure at 8:10 and arrive at 9:27.
• Overtaking
  On the direct road, the passenger car overtakes the slower bus by starting to overtake 20 meters from the bus and after passing it ahead of it again 20 meters away. The car overtakes at a steady speed of 72 km/h, the bus goes at a steady speed of 54 km/h.
• Express train
  International express train drove from Kosice to Teplice. In the first 279 km, the track was repaired, and therefore it was moving at a speed of 10km/h less than it was scheduled to drive. The rest of the 465 km trip has increased the speed by 8 km/h than
• Bus vs. train
  The bus started from point A 10 minutes before the train started from the same place. The bus went an average speed of 49 km/h, train 77 km/h. To point B train and bus arrived simultaneously. Calculate the time of the train journey, if train and bus trave
• Train delay
  Due to a breakdown, the train lost 16 minutes of standing on the track behind Brno. He "eliminated" this delay so that after the start, the 80 km long section went at a speed 10 km/h higher than originally planned. What speed was it and what was it suppos