Question

A man can swim with a speed of 4km/hr in still water. How long does he take to cross a river 1km wide if the river flows steadily at 3km/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?

Answer 1

let velocity of river be Vr = 3km/h

the time (t) taken to cross the river will be:- 

t= river width/speed of man   (time=dis/speed)

t=1/4 hour

 

Now dis=speed*time

distance moved in time t= Vr*t= 3km/h*1/4h=3/4 km

 

So distance travelled by man = 3/4km=750 meter

hope this helps.

Answer 2

Velocity of river cruise= 3 km\h

Time to cross river (t)=riverwidth/speed of man

=1/4 hour

Now, dis.=speed×time

Distance moved on time (t) =vr×t

3km/h ×1/4= 3/4 km

So, distance travelled by man =3/4km

=750 meter