1.

A river is flowing from West to East at a speed of 5 metrper minute. A man on the south bank of the river, caof swimming at 10 metres per minute in still water, wantsto swim across the river in shortest time. He should sin a direction(a) due North(c) 300 West of North (d) 60° East of Northpablewinm(b) 30° East of Nortlh

Answer»

V river = 5m/min

V man = 10 m/minsuppose width of river is x mts

Case 1

if he travels due north

then 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 30

i.e., 2x /31/2 and resultant velocity is 11.2 m/min

so time taken is x / 9.7 mins

Case 2

if he travels due 30 north of east

then 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/min

so time taken is x / 8.7 mins

So case 1 takes least time

he should travel due north(a)


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