Question

A person standing on an open ground hears the sound jet aeroplane,coming from north at an angle ${60}^o$ 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

The correct option is C $\frac{\upsilon }{2}$

$AB=V_p\times t$
$BC=Vt$
$\cos {60}^o=\frac{AB}{BC}$
$\frac{1}{2}=\frac{V_p\times t}{Vt}$
$V_p=\frac{V}{2}$