Question

A boat which has a speed of $5\text{m/s}$ in still water crosses the river of width $25\text{m}$ in 10 seconds. The boat is heading at an angle of $\alpha$ with downstream, where $\alpha$ is equal to

• A. ${150}^{\circ }$
• B. ${120}^{\circ }$
• C. ${90}^{\circ }$
• D. ${60}^{\circ }$

Answer 1

The correct option is A ${150}^{\circ }$


$t=\frac{w}{v\sin \theta }\Rightarrow 10=\frac{25}{5\sin \theta }$
$\sin \theta =\frac{1}{2}\Rightarrow \theta ={30}^{\circ }$
$\therefore \alpha ={180}^{\circ }-\theta ={150}^{\circ }$
$\therefore$ (a)