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Grade: 11
        A river is flowing from west to east at a speed of 5m/s . A man on the south bank of the river capable of swimming at 10m/s in still water wants to swim across the river in the shortest time . In which direction should he swim
one year ago

Answers : (1)

Arun
19665 Points
							
Dear student
 
 

------------> 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.

 

Regards

Arun (askIITians forum expert)

one year ago
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