Question

A boat moving upstream with velocity 3 m/s w.r.t. ground. An observer standing on boat observes that swimmer 'S' is crossing the river perpendicular to the direction of motion of boat. If river velocity is 4m/s & swimmer crosses the river width 100 m in 50 sec then –

• A. Velocity of swimmer w.r.t. ground is $\sqrt{13}$m/s
• B. Velocity of swimmer w.r.t. ground is 2 m/s
• C. Drift of swimmer along river is zero
• D. Drift of swimmer along river will be 50 m

Answer 1

Answer: (B)

Velocity of swimmer w.r.t. ground is 2 m/s

Answer 2

${\overset{\rightarrow}{V}}_{SB}$ = V $\widehat{j}$= ${\overset{\rightarrow}{V}}_{S}$ + 3$\widehat{i}$

\${\overset{\rightarrow}{V}}_{S}$ = $V\widehat{j} - 3\widehat{i}$

V = $\frac{100}{50}$ = 2 m/s

Drift = 50 × 3 = 150 m