Question

A person standing on an open ground hears the sound of a jet aeroplane, coming from north at an angle $60^\circ$ with ground level. But he finds the aeroplane right vertically above his position. If $\upsilon$ is the speed of sound, speed of the plane is :

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

Answer 1

Answer: (C)

$\frac{\upsilon}{2}$

Answer 2

$AB =V_{p}\times t$
$BC = Vt$
$\cos60^{\circ} = \frac{AB}{BC}$
$\frac{1}{2} = \frac{V_{p}\times t}{Vt}$
$V_{p} = \frac{V}{2}$