Question

A river of width $200$ m flows at $5m/s^{-1}$. A man crosses the river in the shear flow and swims with the same velocity, the time taken to cross the river is :

• A. $\frac{200}{5\sqrt{2}}$
• B. $20s$
• C. $25s$
• D. $25\sqrt{2}$

Answer 1

The correct option is B $20s$

Due to the flow, the velocity of man swimming (wrt ground)

adds up; and thus velocity.

$V_{m.g}=V_{flow}+V_{man}=5+5=10$ m/s

Thus, he'll take time, $t=\frac{d}{V_{mg}}=\frac{200}{10}=20s$ to cross the river.