Question

A man rows a boat with a speed of 18 km/hr in north-west direction. The shoreline makes an angle of ${15}^o$ south of west. Obtain the component of the velocity of the boat along the shoreline.

• A. $9km/hr$
• B. $18\frac{\sqrt{3}}{2}km/hr$
• C. $18cos\left({15}^o\right)km/hr$
• D. $18cos\left({75}^o\right)km/hr$

Answer 1

The correct option is A $9km/hr$

Given,

The speed of boat $=18km/hr$ in north west direction. That is velocity makes an angle of ${45}^0$ with west.

We have to find the velocity along shoreline or parallel to river.

We can see in figure that the velocity V makes an angle $(45+15)={60}^0$ with the river.

So,

$Vcos\theta =Vcos{60}^0$

$=18\times \frac{1}{2}$

$=9km/hr$