Question

Два поезда идут навстречу друг другу со скоростью 45 км/ч. Длина каждого поезда 250м. Сколько секунд пройдет с момента встречи машинистов до момента встречи проводников, стоящих у последних дверей последних вагонов?

Answer 1

1) 45+45=90 км/ч скорость с которой приближаются поезда.

2) 250+250=500 м расстояние между последнимидверями последних вогонов, когда встретятся машинисты.

90 км/ч скорость поезда 90 км за 1 мин = 90000 м за 360 сек=25м/сек

90000/360 = 25

3) 500:25=20 сек

Ответ: через 20 сек.

Answer 2

Problem Analysis

We have two trains traveling towards each other at a speed of 45 km/h. The length of each train is 250 meters. We need to calculate the time it takes for the conductors standing at the last doors of the trains to meet after the train drivers meet.

Solution

To solve this problem, we need to calculate the time it takes for the train drivers to meet and then subtract that time from the total time it takes for the conductors to meet.

Let's break down the solution into steps:

1. Calculate the time it takes for the train drivers to meet. 2. Calculate the time it takes for the conductors to meet. 3. Subtract the time for the train drivers from the total time for the conductors to get the final answer.

Step 1: Calculate the time it takes for the train drivers to meet

To calculate the time it takes for the train drivers to meet, we can use the formula:

Time = Distance / Speed

The distance the train drivers need to cover is the sum of the lengths of the two trains, which is 250 meters + 250 meters = 500 meters.

The speed of the train drivers is the combined speed of the two trains, which is 45 km/h + 45 km/h = 90 km/h.

Converting the speed to meters per second, we get:

Speed = 90 km/h * (1000 m/km) / (3600 s/h) = 25 m/s

Plugging the values into the formula, we get:

Time for train drivers = 500 meters / 25 m/s = 20 seconds.

Step 2: Calculate the time it takes for the conductors to meet

To calculate the time it takes for the conductors to meet, we need to consider that they are standing at the last doors of the last cars of their respective trains. This means that they need to cover the entire length of their trains to meet each other.

The distance the conductors need to cover is the sum of the lengths of the two trains, which is 250 meters + 250 meters = 500 meters.

The speed of the conductors is the same as the speed of the train drivers, which is 45 km/h.

Converting the speed to meters per second, we get:

Speed = 45 km/h * (1000 m/km) / (3600 s/h) = 12.5 m/s

Plugging the values into the formula, we get:

Time for conductors = 500 meters / 12.5 m/s = 40 seconds.

Step 3: Calculate the final answer

To calculate the time it takes for the conductors to meet after the train drivers meet, we subtract the time for the train drivers from the total time for the conductors.

Final answer = Time for conductors - Time for train drivers = 40 seconds - 20 seconds = 20 seconds

Therefore, it will take 20 seconds from the moment the train drivers meet until the conductors standing at the last doors of the last cars meet.

Conclusion

From the moment the train drivers meet until the conductors standing at the last doors of the last cars meet, it will take 20 seconds.