The boat went 0.5 hours against the river, the speed of which was 2.8 km / h, and 0.4 hours along the river

| February 11, 2021 | education

The boat went 0.5 hours against the river, the speed of which was 2.8 km / h, and 0.4 hours along the river. In total, the boat covered 17.72 km. Find the speed of the boat against the river.

1. Distance covered by the boat upstream and downstream of the river: S = 17.72 km;

2. Own speed of the boat: Vc km / h;

3. River flow speed: Vp = 2.8 km / h;

4. The boat went against the current: Tnp = 0.5 hours;

5. Time for sailing the boat downstream: Tno = 0.4 hours;

6. Let’s compose the equation of motion:

S = Vnp * Tnp + Vno * Tno =

(Vc – Vp) * Tnp + (Vc + Vp) * Tno =

(Vc – 2.8) * 0.5 + (Vc + 2.8) * 0.4 =

0.9 * Vc – 0.28 = 17.72 km;

7. Own speed of the boat:

Vc = (17.72 + 0.28) / 0.9 = 20 km / h;

8. Speed: Vnp = Vc – Vp = 20 – 2.8 = 17.2 km / h.

Answer: the speed of the boat against the stream of the river is 17.2 km / h.



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