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Standard XII

Physics

Relative Motion in 1D

A swimmer swi...

Question

A swimmer swims in still water at a speed $= 5 k m / h$ . He enters a $200 m$ wide river, having river flow speed $= 4 k m / h r$ at point A and proceeds to swim at an angle of $127^{o}$ with the river flow direction. Another point B is located directly across A on the other side. The swimmer lands on the other bank at a point C, from which he walks the distance CB with a speed $= 3 k m / h r$ . The total time in which he reaches from A to B is

5 m i n u t e s

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4 m i n u t e s

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3 m i n u t e s

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n o n e

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Solution

The correct option is B $4 m i n u t e s$
$t i m e t a k e n t o c r o s s t h e r i v e r i s \frac{0.2}{5 c o s 37^{0}} = \frac{0.2}{4} = .05 h o u r s = 3 m i n h o r i z o n t a l d i s p l a c e m e n t o f t h e m a n i s .05 (4 - 5 s i n 37^{0}) = 0.05 k m t i m e t o c o v e r t h i s d i s t a n c e i s : \frac{0.05}{3} \times 60 = 1 m i n t o t a l t i m e t a k e n = 3 + 1 = 4 m i n$

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Similar questions

Q. A swimmer swims in still water at a speed

= 5 k m / h r

. He enters a

200 m

wide river, having river flow speed

= 4 k m / h r

at point A and proceeds to swim at an angle of

127^{\circ}

with the river flow direction. Another point

B

is located directly across

A

on the other side. The swimmer lands on the other bank at a point

C

, from which he walks the distance

C B

with a speed

= 3 k m / h r

. The total time in which he reaches from

A

B

Q. A swimmer swims in still water at a speed =

5 k m / h r

. He enters a

200 m

wide river, having river flow speed =

4 k m / h r

at a point A and proceeds to swim at an angle of

127^{0}

(sin 37^{*} - 0.6)

with the river flow direction. Another point B is located directly across A on the other side. The swimmer lands on the river bank at a point C. from which he walks the distance CB with a speed=

3 k m / h r

. The total time in which he reach from A to B is

Q. A swimmer swims in still water at a speed of

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Q. A swimmer swims in still water at a speed of

5 k m / h r

. He enters a

200 m

wide river, having a river flow speed of

4 k m / h r

. He proceeds to swim at an angle of

127^{\circ}

with the river flow direction. He reaches directly opposite to the starting point and then swims with the river flow to cover a distance of

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Q. Consider a river

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The correct option is B 4minutestimetakentocrosstheriveris0.25cos370=0.24=.05hours=3minhorizontaldisplacementofthemanis.05(4−5sin370)=0.05kmtimetocoverthisdistanceis:0.053×60=1mintotaltimetaken=3+1=4min