Question
A man can swim with a speed of 4.0 km/hr in still water. How long does he take to cross the river 1.0 km wide if the river flows steadily at 3.0 km/hr and he makes his strokes normal to the river current? How far down the river does he go when he reaches the other bank?
Solution
Rate of flow of swimmer in the still water = 4.0 km/hr
Width of the river = 1.0 km
Rate of flow of river = 3.0 km/hr
Since the swimmer dives in the river normal to the flow of river, therefore time taken by swimmer to cross the river is,
In this time the swimmer will also go down the river by distance BC due to river current.
∴ Distance of the river travelled by the swimmer when he reaches the other bank is given by,
Width of the river = 1.0 km
Rate of flow of river = 3.0 km/hr
Since the swimmer dives in the river normal to the flow of river, therefore time taken by swimmer to cross the river is,
In this time the swimmer will also go down the river by distance BC due to river current.
∴ Distance of the river travelled by the swimmer when he reaches the other bank is given by,
