A man wants to swim across a river of width 200m along the shortest path. If the speed of river stream is 3kmh- 1 and speed of swimmer in still water is 5kmh- 1 , then the time of crossing the river is

Question

A man wants to swim across a river of width 200m along the shortest path. If the speed of river stream is 3kmh- 1 and speed of swimmer in still water is 5kmh- 1 , then the time of crossing the river is (A) 10min (B) 15min (C) 3 min (D) 6min

Tardigrade Admin · Accepted Answer

Speed of swimmer in still water = Speed of swimmer with respect to river. <img class="img-fluid question-image" alt="Solution" src="https://cdn.tardigrade.in/q/nta/p-epwpouswopndgsjx.jpg" /> v⊥=√52 - 32=4kmh- 1 ∴ t=(0.2/4)× 60min=3min

Q. A man wants to swim across a river of width $200 m$ along the shortest path. If the speed of river stream is $3 km h^{- 1}$ and speed of swimmer in still water is $5 km h^{- 1}$ , then the time of crossing the river is

$10 min$

$15 min$

$3 min$

$6 min$

Speed of swimmer in still water = Speed of swimmer with respect to river.

$v_{⊥} = 5^{2} - 3^{2} = 4 km h^{- 1}$
$∴ t = \frac{0.2}{4} \times 60 min = 3 min$

Q. A man wants to swim across a river of width 200m along the shortest path. If the speed of river stream is 3kmh−1 and speed of swimmer in still water is 5kmh−1 , then the time of crossing the river is

10min

15min

3min

6min