A man can swim with a speed of 4km/h in still water.How long does he take to cross 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?

Asked by aruni_maiyer | 22nd Sep, 2010, 10:36: AM

Expert Answer:

The man goes normal to the flow of the current of the river. So , the net velocity of the man will be the resultant of the man's velocity and the perpendicular velocity of the current. Now the man has to cover the width of the river that is 1 km, so the time taken by the man will be,
t = 1/4 = 0.25 seconds.
Vertical distance travelled due to the current = 3*0.25 = 0.75 km
so the man lands at a distance of 0.75 km below from the river.

Answered by  | 22nd Sep, 2010, 10:42: AM

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