A river has a steady speed of 0.360 m/s. A student swims upstream a distance of 1.00 km and swims back to the starting point. (b) How much time is required in still water for the same length swim? (c) Intuitively, why does the swim take longer when there is a current?

The given question is incomplete. The complete question is as follows.

A river has a steady speed of 0.360 m/s. A student swims upstream a distance of 1.00 km and swims back to the starting point.

(a) If the student can swim at a speed of 1.29 m/s in still water, how long does the trip take?

(b) How much time is required in still water for the same length swim?

(c) Intuitively, why does the swim take longer when there is a current?

Explanation:

(a)  Relative velocity of the student while going upstream is as follows.

          (1.29 - 0.360) m/s

         = 0.93 m/s

Now, relative velocity of the student while coming downstream is as follows.

          (1.29 + 0.360) m/s

        = 1.65 m/s

When the student is going upstream then time taken to cover 1 km distance is calculated as follows.

         = 1075.26 sec

When the student is going downstream then time taken by it to cover 1 km distance is as follows.

         = 606.06 sec

Hence, total trip time will be calculated as follows.

     Total trip time = (1075.26 sec + 606.06 sec)

                             = 1681.32 sec

(b)  Time taken in still water is calculated as follows.

             = 1550.38 sec

(c)  When there will be current then there will occur a decrease in relative velocity of the swimmer. Therefore, he will take more time.

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