Question

От речной пристани отправился плот. Через 0,4ч вслед за ним вышла лодка и ещё через 0,4ч обогнала плот на 4 км. Найдите собственную скорость лодки, если скорость течения равна на 2 км/ч

Answer 1

2 км ч -это и скорость плота
2х0.4=0,8 км прошел плот
0,8х2=1,6 км прошел плот
1.6 +4=5.4 прошла лодка
5,4/0,4=13,5 км ч скорость лодки

Answer 2

Problem Analysis

We are given the following information: - A raft departs from a river dock. - After 0.4 hours, a boat leaves the dock and overtakes the raft after another 0.4 hours. - The boat overtakes the raft by 4 km. - The speed of the river current is 2 km/h.

We need to find the speed of the boat.

Solution

Let's assume the speed of the raft is R km/h and the speed of the boat is B km/h.

We can calculate the distance covered by the raft in 0.4 hours as 0.4R km.

Similarly, the distance covered by the boat in 0.4 hours is 0.4B km.

Since the boat overtakes the raft by 4 km, we can set up the following equation:

0.4B - 0.4R = 4 We also know that the speed of the river current is 2 km/h. This means that the effective speed of the boat is the sum of its own speed and the speed of the current, i.e., B + 2 km/h.

The time taken by the boat to cover the distance of 4 km (overtaking the raft) is given by:

4 / (B + 2) hours

Since the boat overtakes the raft after 0.4 hours, we can set up the following equation:

0.4 = 4 / (B + 2) We can solve equations and to find the value of B, which represents the speed of the boat.

Calculation

Let's solve equations and to find the value of B.

From equation we have:

0.4 = 4 / (B + 2)

Cross-multiplying, we get:

0.4(B + 2) = 4

Simplifying, we have:

0.4B + 0.8 = 4

Subtracting 0.8 from both sides, we get:

0.4B = 3.2

Dividing both sides by 0.4, we get:

B = 8

Therefore, the speed of the boat is 8 km/h.

Answer

The speed of the boat is 8 km/h.