The distance between quays A and B is 40 km. From A to B, a motorboat is moving along the river, the speed

| September 10, 2021 | education

The distance between quays A and B is 40 km. From A to B, a motorboat is moving along the river, the speed of which in still water is 18 km / h, and from B to A is another motor boat, the speed of which in still water is 16 km / h. Upon meeting, it turned out that the first boat had been sailing for 1 hour, and the second for 1.5 hours. Find the speed of the river.

1. The distance between the piers is: S = 40 km;

2. Speed of the first boat in still water: V1 = 18 km / h;

3. Own speed of the second boat: V2 = 16 km / h;

4. Time of movement of the first boat before the meeting: T1 = 1 hour;

5. The second boat sailed: T2 = 1.5 hours;

6. The first boat sailed before the meeting: S1 km;

S1 = (V1 + Vp) * T1 = (18 + Vp) * 1 = (18 + Vp) km;

7. The second boat sailed: S2 km;

S2 = (V2 – Vp) * T2 = (16 – Vp) * 1.5 = (24 – 1.5 * Vp) km;

8. Calculate: S km;

S = S1 + S2 = (18 + Vp) + (24 – 1.5 * Vp) =

(42 – 0.5 * Vp) = 40 km;

0.5 * Vp = 42 – 40 = 2 km;

Vp = 2 / 0.5 = 4 km / h.

Answer: the speed of the river is 4 km / h.



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