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 ar $e ______$ an $d _____$ respectively.
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Question

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 ar $e ______$ an $d _____$ respectively.

Options

G1 Physics · Accepted Answer

Convert the speeds: speed of river = 18 km/h = 5 m/s. speed of boat in still water = 36 km/h = 10 m/s. For minimum time to cross a river, the boat should use its full speed component perpendicular to the banks. Time for one crossing: t = width/speed across = 200/10 = 20 s. A round trip requires two crossings: t(round) = 2 × 20 = 40 s. During the total time, the river carries the boat downstream with speed 5 m/s. Therefore the net displacement along the river bank is x = 5 × 40 = 200 m. Correct…