Q 11-03-030NEETJEE MainMedium
A boat whose speed in still water is $5$ m/s must reach the point directly opposite on the other bank of a river flowing at $3$ m/s. The angle between the boat's heading and the direction of the river flow must be
Answer: (C) $127°$
Concept. To go straight across, the boat's upstream component must cancel the river.
Step 1. Heading. $5\sin\alpha = 3 \Rightarrow \alpha = 37°$ upstream of the perpendicular.
Step 2. Angle with the flow. $90° + 37° = 127°$.
Answer. $127°$ (Option C).
Solution by Sreeraj P, M.Sc Physics