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Home » A man can swim with a speed of 4 km/h in still water. How long does he take to cross a river 1 km wide if the river flows steadily at 3 km/h and he makes his strokes normal to the river current? How far down the river does he go when he reaches the other bank?
A man can swim with a speed of 4 km/h in still water. How long does he take to cross a river 1 km wide if the river flows steadily at 3 km/h and he makes his strokes normal to the river current? How far down the river does he go when he reaches the other bank?
CBSE | Class 11 | Motion in a Plane | NCERT | Physics
A man can swim with a speed of 4 km/h in still water. How long does he take to cross a river 1 km wide if the river flows steadily at 3 km/h 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 :

According to the question, speed of the man is

{{v}_{m}}=4km/h

and the width of the river is 1 km

Then the time taken in crossing the river can be determined as follows :

Time=\frac{RiverWidth}{Speed}=\frac{1}{4}h

Time=\frac{1}{4}\times 60=15\min

Speed of the river is

{{v}_{r}}=3km/h

Then the distance covered with flow of river becomes

d={{v}_{r}}\times t=3\times \frac{1}{4}km

d=750m

i

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