Question

Реши задачу: моторная лодка прыла 20км по течению реки и вернулась обратно, потратив на весь путь 2ч 15 минут. Найдите скорость течения реки, если собственная скорость моторной лодки равна 18км/ч.

Answer 1

X км/ час-скорость течения реки; (18+x)-скорость лодки по течению реки; (18-x)- скорость лодки против течения реки. составляем уравнение: 20/(18+x)+20/(18-x)=9/4;  20*4*(18-x)+20*4*(18+x)=9*(18-x)*(18+x); 80*(18-x)+80*(18+x)=9*(324-x^2); 1440-80x+1440+80x=2916-9x^2; 2880-2916= -9x^2; -36= -9x^2; x^2=4; x1= -2(не подходит по смыслу задачи), x2=2. Ответ: скорость течения реки равна 2 км/ час. 

Answer 2

Problem Analysis

To find the speed of the river current, we need to use the formula: speed = distance / time. In this case, the distance is 20 km (one way) and the total time is 2 hours and 15 minutes.

Calculation

Let's convert the time to hours. Since 1 hour is equal to 60 minutes, 15 minutes is equal to 15/60 = 0.25 hours. Therefore, the total time is 2.25 hours.

Now, let's calculate the speed of the boat without the current. The boat traveled a total distance of 40 km (20 km one way and 20 km back). The total time taken was 2.25 hours.

Using the formula speed = distance / time, we can calculate the speed of the boat without the current: speed = 40 km / 2.25 hours = 17.78 km/h.

Since the boat's speed without the current is given as 18 km/h, we can conclude that the speed of the river current is 0.22 km/h.

Answer

The speed of the river current is 0.22 km/h.

Note: The calculation assumes that the speed of the boat remains constant throughout the journey and that there are no other factors affecting the boat's speed.