Q 11-03-084JEE MainJEE Main 2023 (31 Jan, Shift 1)Easy
The speed of a swimmer is $4\ \text{km h}^{-1}$ in still water. If the swimmer makes his strokes normal to the flow of river of width $1\ \text{km}$, he reaches a point $750\ \text{m}$ down the stream on the opposite bank. The speed of the river water is ______ $\text{km h}^{-1}$.
Numerical value type. Enter your answer.
Answer: 3
Time to cross $=\dfrac{1}{4}\ \text{h}$. Drift $=v_r t\Rightarrow0.75=v_r\times\dfrac14\Rightarrow v_r=3\ \text{km h}^{-1}$.
Solution by Sreeraj P, M.Sc Physics