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Ariver 4.0 km wide is flowing at the rat...

Ariver 4.0 km wide is flowing at the rate of 2 km/hr. The minimum time taken by about to cross the river with a speed v= 4 km/hr (in still water) is approximately

A

I hr and 9 minutes

B

2 hr and 7 minutes

C

1hr and 12 minutes

D

2 hr and 25 minutes

Text Solution

Verified by Experts

The correct Answer is:
A
Minimum time is taken when the boat crosses the river at right angles to its flow. The resultant velocity of buat and river should be at right angles to flow of river

AD represents resultant velocity `(AC)^(2)=(CD)^(2)+(AD)^(2) rarr 4^(2)=2^(2)+(AD)^(2)`
`therefore (4)/sqrt(12)=(4)/(2sqrt(3))=(2)/sqrt(3)=1.154` hr =69 min=1 hr 9 min
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