A boat which has a speed of 5km/h in still waters crosses a river of width 1km along the shortest possible path in 15minutes. The speed of the river in km/h is
A
1
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B
3
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C
4
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D
√41
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Solution
The correct option is A3 Speed of boat, vb=5km/h Speed of boat when water flows, vr=114=4km/h Resultant speed v=√vb2−vr2=√52−42=√25−16=√9=3km/h