A river flows west to east at 5 m min⁻¹. A man can swim at 10 m min⁻¹ in still water. In what direction should he swim to take the shortest possible path to the south bank directly opposite?
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Question

A river flows west to east at 5 m min⁻¹. A man can swim at 10 m min⁻¹ in still water. In what direction should he swim to take the shortest possible path to the south bank directly opposite?

G1 Physics · Accepted Answer

To have zero downstream drift, swimmer's upstream component must cancel 5 m min⁻¹. Since swimming speed is 10, sin30°=5/10. Thus he heads 30° west of south, i.e. 120° with downstream direction. Option C.