Question

Допоможіть розв'язати задачу : відстань між пристанями дорівнює 138 цілих шість десятих км швидкість човна в стоячій воді 13 цілих три десятих кілометрів за годину а швидкість течії річки 0,7 км за год скільки потрібно часу моторному човну щоб проплисти від однієї Пристані до іншої та повернутися назад

Answer 1

Длина пристани 138.6 км

Скорость лодки : 13.3 км/ч

Скорость течения : 0.7 км/ч

Так как он ездит вперёд и обратно, соответственно он едет за и против течения.

1. Время за течением = 138.6 : ( 13.3 + 0.7 ) = 9.9 часов

2. Время против течения = 138.6 : ( 13.3 - 0.7 ) = 11 часов

Общее время = 9.9 + 11 = 20.9 часов или 20 часов 54 минуты

Answer 2

Problem Analysis

To solve this problem, we need to calculate the time it takes for a motorboat to travel from one pier to another and return, given the distance between the piers, the speed of the boat in still water, and the speed of the river current.

Given Information

- Distance between the piers: 138.6 km - Speed of the boat in still water: 13.3 km/h - Speed of the river current: 0.7 km/h

Solution

To find the time it takes for the motorboat to travel from one pier to another and return, we need to consider the effect of the river current on the boat's speed.

Let's break down the problem into two parts: 1. Traveling from one pier to another against the current. 2. Returning from the second pier to the first pier with the current.

Traveling Against the Current

When the boat is traveling against the current, its effective speed is reduced by the speed of the current. We can calculate the effective speed using the formula:

Effective Speed = Speed of the boat in still water - Speed of the river current

In this case, the effective speed of the boat is: Effective Speed = 13.3 km/h - 0.7 km/h = 12.6 km/h

To find the time it takes for the boat to travel from one pier to another against the current, we can use the formula:

Time = Distance / Speed

Substituting the values, we get: Time = 138.6 km / 12.6 km/h

Calculating this, we find that it takes the boat approximately 11 hours to travel from one pier to another against the current.

Returning With the Current

When the boat is returning with the current, its effective speed is increased by the speed of the current. We can calculate the effective speed using the formula:

Effective Speed = Speed of the boat in still water + Speed of the river current

In this case, the effective speed of the boat is: Effective Speed = 13.3 km/h + 0.7 km/h = 14 km/h

To find the time it takes for the boat to return from the second pier to the first pier with the current, we can use the formula:

Time = Distance / Speed

Substituting the values, we get: Time = 138.6 km / 14 km/h

Calculating this, we find that it takes the boat approximately 9.9 hours to return from the second pier to the first pier with the current.

Total Time

To find the total time it takes for the boat to travel from one pier to another and return, we add the time taken to travel against the current and the time taken to return with the current:

Total Time = Time to travel against the current + Time to return with the current

Substituting the values, we get: Total Time = 11 hours + 9.9 hours

Calculating this, we find that it takes the boat approximately 20.9 hours to travel from one pier to another and return.

Therefore, the motorboat takes approximately 20.9 hours to travel from one pier to another and return.

Conclusion

The motorboat takes approximately 20.9 hours to travel from one pier to another and return, given the distance between the piers, the speed of the boat in still water, and the speed of the river current.