Question

Single Correct Answer Type
A swimmer wishes to cross a $500$-m river flowing at $5$ km h${}^{-1}$. His speed with respect to water is 3 km h${}^{-1}$. The shortest possible time to cross the river is:

• A. 10 min
• B. 20 min
• C. 6 min
• D. 7.5 min

Answer 1

The correct option is A 10 min

R.E.F image

$V_s=$ velocity of swimmer

w.r.t water = 3 km/hr

$V_w=$ velocity of water = 5 km/hr

For shortest possible time,

$V_s$ should be perpendicular

to river flow

$T_{shortest}=\frac{Distance}{V_S}$

$=\frac{0.5hr}{3km/hr}$

$=\frac{1}{6}hr$

$=10min$

Option (A)