A man can swim with a speed 4km/hr in still water.
(a) How long does he takes to cross a river 1 km wide if the river flows steadily at 3 km/hr and makes his strokes normal to the river current?
(b) How far down the river does he go when he go when he reaches the other bank?

Explanation

Speed of man `=4 km h^(-1)`
Distance travelled =1 km
Speed of river `=3 km h^(-1)`
Time taken by the man to cross the river
`t=("width of the river ")/(Speed) =(1.0 km )/( 4.0 km h^(-1))=(1)/(4)h =15 min`
`therefore` Distance travelled by man along the river in
15 min `(or (1)/(4) h )` is given by s=velocity of the river `xx ` time `vt= 3 km h^(-1) xx(1)/(4)h =(3)/(4) km =750` m .