A river is flowing from west to east direction with speed of 9 km h -1 . If a boat capable of moving at a maximum speed of 27 km h -1 in still water, crosses the river in half a minute, while moving with maximum speed at an angle of 150 ° to direction of river flow, then the width of the river is

Physics · Motion in Plane

JEE Main 2025 — 2 April, Morning Shift — Question 48

A river is flowing from west to east direction with speed of $9 \mathrm{~km} \mathrm{~h}^{-1}$ . If a boat capable of moving at a maximum speed of $27 \mathrm{~km} \mathrm{~h}^{-1}$ in still water, crosses the river in half a minute, while moving with maximum speed at an angle of $150^{\circ}$ to direction of river flow, then the width of the river is

Option A:
112.5 m
Correct
Option B:
75 m
Option C:
300 m
Option D:
$112.5 \times \sqrt{3} \mathrm{~m}$

Answer: A

Step-by-step solution

$t=\frac{w}{v_{b} \cos (60)}$

\begin{aligned} w & =t v_{b} \cos (60) & =30 \times 27 \times \frac{5}{18} \times \frac{1}{2} & =112.5 \mathrm{~m} \end{aligned}

Answer key and solution verified before publishing.

Practise Motion in Plane

Start with this question, then two more from the same chapter — with a tutor that explains every step. Free.

Solve a similar one free

Exam: JEE Main 2025
Paper: 2 April, Morning Shift
Subject: Physics
Chapter: Motion in Plane
Topic: Relative motion in Two Dimension