Question

A boat takes 1 hour longer to go 36 km up a river than to return .If the river flows at 3km/hr , find the rate at which the boat travels in still water

Answer 1

Answer:

15kmph

Step-by-step explanation:

rate at which water is flowing is 3kmph

And velocity of boat in still water be Vb

In Upstream river opposes the motion,

so relative velocity is Vb-3

and time it takes = 36÷[Vb-3]

In down stream water supports the motion,

so relative velocity is Vb+3

and time is 36÷[Vb+3]

difference in time is given as 1 hour so

$\frac{36}{vb - 3} - \frac{36}{vb + 3} \\ = 1 \\ = > \frac{36 \times 6}{ {vb}^{2} - 9 } = 1 \\ = > {vb }^{2} = 225 \\ = > vb = 15kmph$