Question

River is flowing at $3\text{km/h}$ in the west direction and you can swim at a maximum speed of $5\text{km/h}$, then in which direction must you swim so that you end up swimming perpendicular to the bank?

• A. ${\sin }^{-1}(\frac{4}{5})$
• B. ${\sin }^{-1}(\frac{3}{5})$
• C. ${\cos }^{-1}(\frac{3}{5})$
• D. ${\tan }^{-1}(\frac{3}{5})$

Answer 1

The correct option is B

${\sin }^{-1}(\frac{3}{5})$

Since question is saying that I have to swim in perpendicular to the bank, so, resultant should be perpendicular to river flow direction as shown in below diagram.


So, from the above diagram,

$\sin \theta =\frac{3}{5}$

$\therefore \theta ={\sin }^{-1}(\frac{3}{5})$

Hence, option $\left(\text{D}\right)$ is the correct answer.