JEE PYQ: Waves And Sound Question 47
Question 47 - 2019 (12 Jan Shift 2)
A person standing on an open ground hears the sound of a jet aeroplane, coming from north at an angle 60$°$ with ground level. But he finds the aeroplane right vertically above his position. If $v$ is the speed of sound, speed of the plane is:
(1) $\frac{\sqrt{3}}{2}v$
(2) $\frac{2v}{\sqrt{3}}$
(3) $v$
(4) $\frac{v}{2}$
Show Answer
Answer: (4)
Solution
Distance, PQ $= v_p \times t$ (Distance = speed $\times$ time)
Distance, QR $= Vt$
$\cos 60° = \frac{PQ}{QR}$
$\frac{1}{2} = \frac{v_p \times t}{V \cdot t} \Rightarrow v_p = \frac{v}{2}$
BETA
