Question

A man can swim with a speed of `4kmh^(-1)` in still water. He crosses a river 1km wise that flows steadly at `3kmh^(-1)`. If he makes his strokes normal to the river current, how far down the river does he go when he reaches the other bank?
A. `800m`
B. `900m`
C. `400m`
D. `750m`

Answer 1

(d) Given speed of man `v_(m)=4km//h`

Speed of river `v_(r)=3km//h`
Width of the river `d=1km`
Time taken by the man to cross the river,
`t=("Width of the river")/("Speed of the man")=(1km)/(4km//h)=1/4 h = 1/4 xx60=15min`
Distance travelled along the river `=v_(r)xxt`
`=3xx1/4=3/4km=3000/4=750km`