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  4. The speed of a swimmer is 4 km h -1 in still water. If the swimmer makes his strokes normal to the flow of river of width 1 km, he reaches a point 750 m down the stream on the opposite bank. The speed of the river water is km h -1

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Q. The speed of a swimmer is $4 \,km\, h ^{-1}$ in still water. If the swimmer makes his strokes normal to the flow of river of width $1 \,km$, he reaches a point $750 \,m$ down the stream on the opposite bank. The speed of the river water is ___ $km h ^{-1}$

JEE MainJEE Main 2023Motion in a Plane

Solution:

image
time to cross the River width $\omega=1000 \,m$
$\text { is }=\frac{1 km }{4 km / h }$
Drift $x=V m / g \times t$
Where $Vm / g$ is velocity of River w.r. to ground.
$ x = Vm / g \times \frac{1}{4}=750 m =\frac{3}{4} km$
$ Vm / g =3 \,km / hr$