Question

Лодка плыла по течению 3,5ч,а против течения-2,5ч.Всего лодка проплыла 81км/ч.Скорость течения реки 1,8км/ч.Найдите собственную скорость лодки.

Answer 1

Скорость движения лодки - Х км/час

Тогда

Путь=скорость*время

3,5*(Х+1,8)+2,5*(Х-1,8)=81

3,5*Х+6,3+2,5*Х-4,5=81

6*Х=81-1,8=79,2

Х=79,2/6=13,2 км/час - скорость лодки

 

Проверяем:

3,5*(13,2+1,8)+2,5*(13,2-1,8)=81

3,5*15+2,5*11,4=81

52,5+28,5=81

Answer 2

Problem Analysis

We are given the following information: - The boat travels downstream for 3.5 hours. - The boat travels upstream for 2.5 hours. - The total distance covered by the boat is 81 km. - The speed of the river current is 1.8 km/h.

We need to find the speed of the boat in still water.

Solution

Let's assume the speed of the boat in still water is x km/h.

When the boat is traveling downstream, it gets a boost from the river current, so its effective speed is the sum of its own speed and the speed of the current. Therefore, the distance covered downstream is given by:

Distance downstream = (speed of the boat + speed of the current) × time downstream

Substituting the given values, we have:

Distance downstream = (x + 1.8) × 3.5

Similarly, when the boat is traveling upstream, it has to overcome the resistance of the river current, so its effective speed is the difference between its own speed and the speed of the current. Therefore, the distance covered upstream is given by:

Distance upstream = (speed of the boat - speed of the current) × time upstream

Substituting the given values, we have:

Distance upstream = (x - 1.8) × 2.5

Since the total distance covered by the boat is 81 km, we can write the equation:

Distance downstream + Distance upstream = 81

Substituting the above expressions for the distances, we have:

(x + 1.8) × 3.5 + (x - 1.8) × 2.5 = 81

Now, we can solve this equation to find the value of x, which represents the speed of the boat in still water.

Let's solve the equation step by step:

(x + 1.8) × 3.5 + (x - 1.8) × 2.5 = 81

Simplifying the equation:

3.5x + 6.3 + 2.5x - 4.5 = 81

Combining like terms:

6x + 1.8 = 81

Subtracting 1.8 from both sides:

6x = 79.2

Dividing both sides by 6:

x = 13.2

Therefore, the speed of the boat in still water is 13.2 km/h.

Answer

The speed of the boat in still water is 13.2 km/h.