Question

Пароход плыл 5 часов по течению реки и 3 часа против течения. С какой средней скоростью он плыл, если его собственная скорость ровна U км/час , а скорость течения реки - 2 км/час ?(U-=28; 29,7; 35,5) помогите решить , желательно полное решение. 6 класс

Answer 1

Это типовая задача: средняя скорость находится при делении всего пути на все время. Чтобы найти весь путь надо сложить два участка .Первый (v+2)*5 и второй (v-2)*3. Общее время 5+3=8.Откуда получаем vсредн= [(v+2)*5 +(v-2)*3] делить на 8.Скобки раскройте, пожалуйста сами, чтобы не тратить на это много времени.

Answer 2

Problem Analysis

We are given that a steamboat traveled for 5 hours with the current of a river and 3 hours against the current. We need to find the average speed of the steamboat if its own speed is U km/h and the speed of the river current is 2 km/h.

Solution

To solve this problem, we can use the formula: average speed = total distance / total time.

Let's assume the distance traveled with the current is D1 and the distance traveled against the current is D2.

The time taken to travel with the current is 5 hours, so the distance traveled with the current can be calculated as: D1 = (U + 2) * 5.

The time taken to travel against the current is 3 hours, so the distance traveled against the current can be calculated as: D2 = (U - 2) * 3.

The total distance traveled is the sum of the distances traveled with and against the current: total distance = D1 + D2.

The total time taken is the sum of the time taken to travel with and against the current: total time = 5 + 3.

Finally, we can calculate the average speed using the formula: average speed = total distance / total time.

Let's substitute the given values and solve for the average speed.

Calculation

Given: - U = 28 km/h (as per the problem statement)

Using the formulas mentioned above, we can calculate the average speed as follows:

D1 = (U + 2) * 5 = (28 + 2) * 5 = 30 * 5 = 150 km

D2 = (U - 2) * 3 = (28 - 2) * 3 = 26 * 3 = 78 km

Total distance = D1 + D2 = 150 + 78 = 228 km

Total time = 5 + 3 = 8 hours

Average speed = total distance / total time = 228 / 8 = 28.5 km/h

Therefore, the steamboat traveled with an average speed of 28.5 km/h.

Answer

The steamboat traveled with an average speed of 28.5 km/h.

Explanation

The average speed is calculated by dividing the total distance traveled by the total time taken. In this case, the steamboat traveled for 5 hours with the current and 3 hours against the current. By substituting the given values into the formula, we found that the average speed is 28.5 km/h.