Question

A river is flowing from west to east at a speed of

5 m./min. A man on the south bank of the river,

capable of swimming at 10 m./min. in still water,

wants to swim across the river in shortest time. He

should swim in a direction-

[1] Due north [2] 300

east of north

[3] 300

west of north [4] 600

east of north​

Answer 1

Explanation:

river = 5m/min V man = 10 m/minsuppose width of river is x mtsCase 1if he travels due norththen his resultant velocty ( due to velocity of downstream of water) acts 30 north of east and the distane to be covered to reach the other bank increses to = x/cos 30i.e., 2x /31/2 and resultant velocity is 11.2 m/minso time taken is x / 9.7 minsCase 2if he travels due 30 north of eastthen his resultant velocty ( due to velocity of downstream of water) actsdue north and the distane to be covered to reach the other bank will be x mts and resultant velocity is 8.7 m/minso time taken is x / 8.7 minsSo case 1 takes least timehe should travel due North(a)

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