Question

Скорость моторной лодки в стоячей воде 15 км/ч, а скорость течения реки 3 км/ч. Сколько времени потратит моторная лодка на движение от одной пристани до другой и обратно, если расстояние между пристанями 36 км?

Answer 1

Скорость лодки по течению равна 18 км в час
против течения 12 км в час
t=s/v. зн t1=36/18=2
t2=36/12=3
t=t1+t2, t=2+3=5

Answer 2

Answer in detail. The speed of a motorboat in still water is 15 km/h, and the speed of the river current is 3 km/h. How much time will the motorboat take to move from one pier to another and back, if the distance between the piers is 36 km?

To answer this question, we need to find the effective speed of the motorboat when it moves upstream and downstream. The effective speed is the sum of the speed of the motorboat and the speed of the current, with the sign depending on the direction of the current.

When the motorboat moves upstream, the current is opposite to its direction, so the effective speed is 15 - 3 = 12 km/h. When the motorboat moves downstream, the current is in the same direction, so the effective speed is 15 + 3 = 18 km/h.

The time taken by the motorboat to move a certain distance is the ratio of the distance and the effective speed. Therefore, the time taken by the motorboat to move from one pier to another and back is:

$$t = \frac{36}{12} + \frac{36}{18} = 3 + 2 = 5 \text{ hours}$$

Hence, the motorboat will take 5 hours to complete the round trip.