Motion in a Plane

Question : 13

Total: 32

A man can swim with a speed of 4.0 km h‌–1 in still water. How long does he take to cross a river 1.0 km wide if the river flows steadily at 3.0 km h‌–1 and he makes his strokes normal to the river current? How far down the river does he go when he reaches the other bank?

Solution:

Speed of man, vx=4 km h‌–1
Distance travelled = 1 km
Speed of river = 3 km h‌–1If t = time taken to cross the river
Then, t=

Distance

Speed

1km

4km∕h−1

hour =15 minutes
The man is carried down by stream with velocity of river water.
∴ Distance travelled by man in 15 min(or‌

‌h) is
=3kmh−1×

h=750m

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