How long will it take to go on a boat a distance of 1.5 km there and back along the river, the speed of which is V = 2 km / h

| September 1, 2021 | education

How long will it take to go on a boat a distance of 1.5 km there and back along the river, the speed of which is V = 2 km / h and along the lake if the speed of the boat relative to the water is V2 = 2 km / h.

S = 1.5 km.

VT = 2 km / h

Vк = 8 km / h.

t -?

The time of movement of the boat t will be the sum: t = t1 + t2, where t1 is the time of movement of the boat downstream, t2 is the time of movement of the boat against the current.

The time of boat movement downstream t1 is expressed by the formula: t1 = S / V1, where V1 is the speed of the boat downstream.

V1 = Vk + Vt.

t1 = S / (Vk + Vt).

t1 = 1.5 km / (8 km / h + 2 km / h) = 0.15 h.

The time of movement of the boat against the current t2 is expressed by the formula: t2 = S / V2, where V2 is the speed of movement of the boat against the current.

V2 = Vk – Vt.

t2 = S / (Vk – Vt).

t2 = 1.5 km / (8 km / h – 2 km / h) = 0.25 h.

t = 0.15 h + 0.25 h = 0.4 h = 24 min.

Answer: the boat will take time t = 24 minutes to sail there and back.



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