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?

Options

A. 500 m, 15 min
B. 600 m, 0.25 min
C. 750 m, 15 min
D. 850 m, 0.25min

Answer

C

Explanation

Time to cross the river,
`t=("Widht of river")/("Speed of man")=(1km)/(4kmh^(-1))=(1)/(4)h`
Distance moved along the river in time t,
`s=v_(r)xxt=3kmh^(-1)xx(1)/(4)h=(3)/(4)km=750m`