# 19. A swimmer can swim at a speed of 0.70 ms-1 with respect to the water. She wants to cross a river 50 m wide and having a current of 0.50 ms-1. a) In what direction must she swim in order to reach the other bank at a point directly across where she started from? How rapidly will she increase her distance from the near bank? How long will it take her to cross? b) If instead, she decides to cross in the shortest possible time, how should she swim? Find the time taken to cross?

Aman Bansal
592 Points
13 years ago

Dear Dennis,

distance = speed * time

downstream
1.2km = speed * 20 minute

speed = 1.2/20 (downstream) = .06 km/min * 1000m/km * 1 min/60sec = 1 m/s downstream

Relative to the stream, 1 m/s - .3 m/s = .7 m/s
therefore
upstream speed = .7 m/s - .3 m/s = .4 m/s

time = distance/speed = 1.2 km / (.4 m/s * km/1000m * 60s/min) = 50 min

total time = 50 + 20 = 70 minutes

Best Of luck

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Thanks

Aman Bansal