A man crosses the river in minimum time of 10min with a drift of 120m. If he crosses the river in shortest path he takes 12.5min. What is his swimming speed?

Question

A man crosses the river in minimum time of 10min with a drift of 120m. If he crosses the river in shortest path he takes 12.5min. What is his swimming speed? (A) 20mmin- 1 (B) 15mmin- 1 (C) 10mmin- 1 (D) 5mmin- 1

Tardigrade Admin · Accepted Answer

For shortest time t1=(d/v)=10⇒ d=10v and x=vRt1 120=vR10 ⇒ vR=12mmin- 1 For shortest path t2=(d/√v2 - vR2) <img class="img-fluid question-image" alt="Solution" src="https://cdn.tardigrade.in/q/nta/p-r5rhfhbsqxofuvfs.jpg" /> 12.5=(10 v/√v2 - 122)⇒ √v2 - 122=0.8v v2-122=0.64v2 0.36v2=144 v2=400 v=20mmin- 1

Q. A man crosses the river in minimum time of $10 min$ with a drift of $120 m .$ If he crosses the river in shortest path he takes $12.5 min .$ What is his swimming speed?

$20 mmi n^{- 1}$

$15 mmi n^{- 1}$

$10 mmi n^{- 1}$

$5 mmi n^{- 1}$

Q. A man crosses the river in minimum time of 10min with a drift of 120m. If he crosses the river in shortest path he takes 12.5min. What is his swimming speed?

20mmin−1

15mmin−1

10mmin−1

5mmin−1

For shortest time t1​=vd​=10⇒d=10v and x=vR​t1​ 120=vR​10 ⇒vR​=12mmin−1 For shortest path t2​=v2−vR2​​d​ 12.5=v2−122​10v​⇒v2−122​=0.8v v2−122=0.64v2 0.36v2=144 v2=400 v=20mmin−1

Q. A man crosses the river in minimum time of $10 min$ with a drift of $120 m .$ If he crosses the river in shortest path he takes $12.5 min .$ What is his swimming speed?

$20 mmi n^{- 1}$

$15 mmi n^{- 1}$

$10 mmi n^{- 1}$

$5 mmi n^{- 1}$