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NEET Physics QUESTION #7294
Question 1

A swimmer's speed in still water is $20\text{ m/s}$. River water flows eastward at $10\text{ m/s}$. He stands on the south bank and wishes to cross via the shortest path. The angle his strokes should make with north is:

  • $30°$ west✔️
  • $0°$
  • $60°$ west
  • $45°$ west
Correct Answer Explanation

To travel straight north, the swimmer must aim upstream (westward) to cancel river drift.

If $\phi$ is the angle west of north:

$v_{\text{swim}}\sin\phi = v_{\text{river}} \Rightarrow 20\sin\phi = 10 \Rightarrow \sin\phi = \dfrac{1}{2} \Rightarrow \phi = \mathbf{30°}$ west of north