A boat crossing a river moves with a velocity $v$ relative to still water. The river is flowing with a velocity $v / 2$ with respect to the bank. The angle with respect to the flow direction with which the boat should move to minimize the drift is-

• A

  $30^{\circ}$
• B

  $60^{\circ}$
• C

  $150^{\circ}$
• Correct answer
  D

  $120^{\circ}$

Solution

To minimize the drifting $\begin{array}{l} \sin \theta=\frac{\mathrm{v}_{\mathrm{w}}}{\mathrm{v}_{\mathrm{bw}}}=\frac{1}{2} \\ \theta=30^{\circ} \\ 90^{\circ}+\theta=120^{\circ} \end{array}$

Hence, the correct answer is option: 'D'.