Question

Лодка плыла 4 ч по течению реки а затем 5 ч против течения. Найдите собственную скорость лодки(т.е. скорость в стоячей воде),если известно что скорость течения реки равна 3км/ч. а всего лодкой пройдено 30​

Answer 1

Ответ:  3 2/3 км/час.  

Объяснение:

х км/час - собственная скорость лодки.

х+3 -  км/час - скорость  по течению.

х-3 -  км/час - скорость  против  течения.

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Если по воде не плавают, а ходят, то:

Путь по течению s1=vt=4*(x+3) км.

Путь против течения s2=5(x-3) км.

S=30 км.  s1+s2=30 км.

4(x+3) + 5(x-3)=30;

4x+12+5x-15=30;

9x=30+15-12;

9x= 33;

x=33/9=11/3 =3 2/3 км/час.  

Answer 2

Finding the Boat's Speed in Still Water

To find the boat's speed in still water, we need to consider the time it took for the boat to travel both with and against the current.

Given: - The boat traveled downstream (with the current) for 4 hours. - The boat traveled upstream (against the current) for 5 hours. - The speed of the river's current is 3 km/h. - The total distance traveled by the boat is 30 km.

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

Calculating the Boat's Speed

When the boat is traveling downstream, the effective speed is the sum of the boat's speed in still water and the speed of the current. Therefore, the boat's effective speed downstream is (x + 3) km/h.

When the boat is traveling upstream, the effective speed is the difference between the boat's speed in still water and the speed of the current. Therefore, the boat's effective speed upstream is (x - 3) km/h.

Using the formula: distance = speed × time, we can calculate the distances traveled by the boat in both directions.

- Distance downstream: (x + 3) km/h × 4 h = 4x + 12 km - Distance upstream: (x - 3) km/h × 5 h = 5x - 15 km

Since the total distance traveled by the boat is 30 km, we can set up the equation:

(4x + 12) km + (5x - 15) km = 30 km

Simplifying the equation:

9x - 3 km = 30 km

9x = 33 km

x = 33/9 km/h

Therefore, the boat's speed in still water is approximately 3.67 km/h.

Please note that the calculations provided are based on the information given and may vary slightly depending on the specific context of the problem.