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Help me understand! - Kinematics - JEE Main-2

The stream of a river is flowing with a speed of 2\: km/h. A swimmer can swim at a speed of 4\: km/h . What should be the direction of the swimmer with respect to the flow of the river to cross the river straight ?

 

  • Option 1)

    90^{\circ}         

  • Option 2)

    150^{\circ}

  • Option 3)

    120^{\circ}

  • Option 4)

    60^{\circ}

 
Answers (1)
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\vec{v}_{mr}=\vec{v}_{m}-\vec{r}

v_{m}=\vec{v}_{mr}+\vec{r}

\sin\theta =\frac{\left | \vec{v}_{r} \right |}{\left | v_{mr} \right |}=\frac{2}{4}=\frac{1}{2}

        \theta =30^{\circ}

Now, the angle with the downstream is 

   =90^{\circ}+30^{\circ}

    =120^{\circ}

 


Option 1)

90^{\circ}         

Option 2)

150^{\circ}

Option 3)

120^{\circ}

Option 4)

60^{\circ}

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