A man can swim with a speed of 4 km/h in still water. How long does he take to cross a river 1 km wide if the river flows steadily at 3 km/h and he makes his strokes normal to the river current? How far down the river does he go when he reaches the other bank?
Since he makes his strokes normal to the river current, the movement of the river will have no effect on the time of crossing the bank. The time will be, T=SpeedDistance=41hr=0.25hr=15min. In the same time, he will go down by Distance=Speed x time=3km/hr x 0.25hr=0.75km=750m
