A river of width 200 m is flowing from west to east with a speed of… | JEE Main 2026 (21 Jan, Shift 2)

Q2JEE Main 2026 · 21 JAN · SHIFT 2Medium

Relative Velocity in Two Dimensions

A river of width 200 m is flowing from west to east with a speed of 18 km/h. A boat, moving with speed of 36 km/h in still water, is made to travel one-round trip (bank to bank of the river). Minimum time taken by the boat for this journey and also the displacement along the river bank are ______ and ______ respectively.

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Answer: (c)

Minimum time: head perpendicular to flow. $v_b = 36\text{ km/h} = 10\text{ m/s}$ , $v_r = 18\text{ km/h} = 5\text{ m/s}$ .
One crossing: $t = \frac{200}{10} = 20\text{ s}$ ; round trip $= 40\text{ s}$ .
Drift each way $= 5 \times 20 = 100\text{ m}$ downstream; both crossings drift east, total $200\text{ m}$ .
So the answer is (c) 40 s and 200 m.

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Relative Velocity in Two Dimensions question from JEE Main 2026 (21 Jan, Shift 2)

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