Question

A boat moves with a speed of $5km/h$ relative to water in a river flowing with a speed of $3km/h$ and a width of $1km$. The minimum time taken around a round trio is

• A. $5$ minutes
• B. $20$ minutes
• C. $30$ minutes
• D. $60$ minutes

Answer 1

The correct option is C $30$ minutes

Given,

Width of river is $1km$

Relative velocity w.r.t river, $5km{h}^{-1}$

Velocity of river, $3km{h}^{-1}$

$\text{t}=\frac{\text{width}}{\text{velocity}\text{of}boat}=\frac{1}{\sqrt{5^2-3^2}}=\frac{1}{4}$

$t=0.25hr$

For round trip

Total time, $T=2t=2\times 0.25=0.5hr$

$T=30min$

Hence, time taken for round trip is $30min$