Q. 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 :
Solution:
$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} $
