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A man crosses the river perpendicular to river flow in time t seconds and travels an equal distance down the stream in T seconds. The  ratio  of  man's speed in still water to the speed of river water will be :

Option: 1

\frac{t^{2}-T^{2}}{t^{2}+T^{2}}


Option: 2

\frac{T^{2}-t^{2}}{T^{2}+t^{2}}


Option: 3

\frac{t^{2}+T^{2}}{t^{2}-T^{2}}


Option: 4

\frac{T^{2}+t^{2}}{T^{2}-t^{2}}


Answers (1)

best_answer

 

 

Let the velocity of man in still water be v and that of water with respect to the ground be u.

       So The velocity of man perpendicular to river flow with respect to ground =  \sqrt{v^{2}-u^{2}}

Velocity of man downstream = v + u

As given, \sqrt{v^{2}-u^{2}}\; t=\left ( v+u \right )T

\Rightarrow \left ( v^{2}-u^{2} \right )t^{2}=\left ( v+u \right )^{2}T^{2}

\Rightarrow \left ( {v-u} \right )t^{2}=\left ( v+u \right )T^{2}

\therefore \frac{v}{u}=\frac{t^{2}+T^{2}}{t^{2}-T^{2}}

Posted by

rishi.raj

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