Introduction to 2D Motion

Q. A person standing on open ground hears the sound of a jet airplane, coming from the north at an angle ${30}^{\circ }$ with the horizontal. But he finds the airplane vertically above his position. If $v$ is the speed of sound, then speed of the plane is

1. $\frac{\sqrt{3}}{2}v$
2. $v$
3. $\frac{2}{\sqrt{3}}v$
4. $\frac{v}{2}$