Question

Мужчина увидел на расстоянии 60м от себя плывущее по реке бревно, которое приближалось к месту, где купались дети, и поплыл бревну навстречу со скоростью 20м/мин. Через 2,5мин он поймал бревно, затем оттащил его к берегу. Какова скорость течения реки? И с какой скоростью мог бы плыть этот мужчина при таких же затратах сил, если бы плыл по озеру?

Answer 1

Ответ:

4м/мин

Пошаговое объяснение:

20×2,5=50мин

60-50=10

скорость течения=10:2,5=4м/мин

Answer 2

Problem Analysis

In this problem, we are given that a man sees a log floating in a river at a distance of 60 meters from him. The log is approaching the area where children are swimming. The man starts swimming towards the log at a speed of 20 meters per minute. After 2.5 minutes, he catches the log and then drags it to the shore. We need to determine the speed of the river's current and the speed at which the man could swim if he were in a lake.

Solution

Let's assume the speed of the river's current is v meters per minute.

To solve this problem, we can use the concept of relative velocity. The man is swimming towards the log, so his effective speed is the sum of his swimming speed and the speed of the river's current.

Let's denote the speed of the man as vm and the speed of the log as vl.

We are given the following information: - Distance between the man and the log: 60 meters - Speed of the man: 20 meters per minute - Time taken by the man to catch the log: 2.5 minutes

Using the formula distance = speed × time, we can calculate the distance the man traveled to catch the log.

The distance traveled by the man is equal to the distance between the man and the log when he started swimming, minus the distance between the man and the log when he caught it.

Let's calculate the distance traveled by the man: ``` distance_traveled = distance_start - distance_end ``` where ``` distance_start = 60 meters distance_end = 0 meters (since the man caught the log) ```

Substituting the values, we get: ``` distance_traveled = 60 - 0 = 60 meters ```

Now, we can calculate the time taken by the man to catch the log: ``` time_taken = 2.5 minutes ```

Using the formula speed = distance / time, we can calculate the effective speed of the man: ``` vm + v = distance_traveled / time_taken ```

Substituting the values, we get: ``` 20 + v = 60 / 2.5 ```

Simplifying the equation, we find: ``` 20 + v = 24 v = 24 - 20 v = 4 meters per minute ```

Therefore, the speed of the river's current is 4 meters per minute.

To calculate the speed at which the man could swim if he were in a lake, we can use the same formula: ``` vm + 0 = distance_traveled / time_taken ```

Substituting the values, we get: ``` vm = 60 / 2.5 ```

Simplifying the equation, we find: ``` vm = 24 meters per minute ```

Therefore, the speed at which the man could swim if he were in a lake is 24 meters per minute.

Conclusion

The speed of the river's current is 4 meters per minute. If the man were swimming in a lake, he could swim at a speed of 24 meters per minute.