Question

To cross a river of width 'D' in minimum time which of the following condition must be fulfilled. Symbols have usual meaning

• A. $V_{m,w} \perp V_w$
• B. $V_m \perp V_w$
• C. $V_w$ should be parallel to $V_{mw}$
• D. None

Answer 1

Answer: (A)

$V_{m,w} \perp V_w$

Answer 2

To cross a river in minimum time, the component of the man's velocity perpendicular to the river flow must be maximized. This component is derived from the man's velocity relative to the water ($V_{m,w}$). By directing $V_{m,w}$ exactly perpendicular to the river flow ($V_w$), the entire magnitude of $V_{m,w}$ contributes to crossing the width, thus minimizing the time.