Water of a river is flowing with a speed of 5 km/hr. A
swimmer can swim at a speed of 10 km/hr in still water.
In what direction the swimmer starts swimming in the
river so as to cross the river: (i) by least possible path (ii)
in least possible time?
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Answer: This may help you
Explanation:
When his head is making angle θ with the flow the net velocity can be distributed as follows:
In order the find the time taken to cross the river.
Consider only vertical correspond
So,
speed (v)=
time(t)
disfance(d)
⇒ 3sinθ km/he=
t
500 ve
t=
3sinθ km/hr
500 ve
(b) To take with time to cross the river, his head should walk right angle with the follow of water, so, θ=90
o
Then, t=
3sinθ
30
=
sin90
o
10
=10 min
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