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The speed of boat is 5 kmh^(-1) in still...

The speed of boat is `5 kmh^(-1)` in still water. It crosses a river of width 1 km along the shortest possible path in 15 min. Then, velocity of river will be

A

`3` km/hr

B

`4` km/hr

C

`5` km/hr

D

`2` km/hr

Text Solution

Verified by Experts

The correct Answer is:
A

`V_(mr)=5` km/hr `t=15` min
`t=(d)/(sqrt(V_("mr")^(2)-V_(t)^(2)))implies(15)/(60)=(1)/(sqrt(25-V_(t)^(2)))`
`implies4=sqrt(25-V_(t)^(2))impliesV_(t)^(2)=25-16impliesV_(t)^(2)=9`
`implies V_(t)=3` km/hr
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