A fish swims in a river that flows at 5 mihr Assume the fish

A fish swims in a river that flows at 5 mi/hr. Assume the fish\'s speed relative to the water (as if the water were still) is 8 mi/hr. What is the fish\'s speed relative to the river bank, if it swims downstream, and upstream

Solution

the speed of river flow = 5 mi / hr

the speed of fish in still water = 8 mi/ hr

(a) if Vd be the speed of the fish with respect the bank in downstream (in downstream the speed of the fish and the river are in same direction)

               Vd = speed of the fish in still water + speed of the river flow

                     = 8 mi/ hr+ 5 mi/hr

                     = 13 mi/hr.

(b) if Vu be the speed of the fish with respect the bank in upstream (in upstream the speed of the fish and the river are in opposite direction)

                         Vu = speed of the fish in still water - speed of the river flow

                              = 8mi/h - 5mi/hr

                              = 3mi/hr