Question

A ship is travelling due east at $10km/h$. A ship heading ${30}^{\circ }$ east of north is always due north from the first ship. The speed of the second ship in $km/h$ is:

• A. $20\sqrt{2}$
• B. $20\sqrt{\frac{3}{2}}$
• C. $20$
• D. $\frac{20}{\sqrt{2}}$

Answer 1

The correct option is C $20$

Let the speed of ship be $x$,
Thus $x\times cos60=10$ (since the ship is always north of the ship due east)
thus $\frac{x}{2}=10$
Therefore, speed of the second ship, $x=20km/h$