Question

A boatman can row with a speed of $10km/h$ in still water. The river flow steadily at $5km/h$ and the width of the river is $2km$. If the boatman cross the river with reference to minimum distance of approach then time elapsed in rowing the boat (in hours) will be

• A. $\frac{2\sqrt{3}}{5}$
  
• B. $\frac{2}{5\sqrt{3}}$
• C. $\frac{3\sqrt{2}}{5}$
• D. $\frac{5\sqrt{2}}{3}$

Answer 1

Answer: (B)

$\frac{2}{5\sqrt{3}}$

$t=\frac{d}{\sqrt{v_{mr}^2-v_r^2}}=\frac{2}{\sqrt{100-25}}=\frac{2}{\sqrt{75}}=\frac{2}{5\sqrt{3}}h$