Question

Two factories are sounding their sirens at $800\, Hz$. A man goes from one factory to other at a speed of $2\, m/s$. The velocity of sound is $320\, m/s$. The number of beats heard by the person in one second will be :

• A. 2
• B. 4
• C. 8
• D. 10

Answer 1

Answer: (D)

10

Answer 2

Number of beats, $b$ is
$b =\frac{2 V _{ o } n }{ V _{ s }}$
$=\frac{2 \times 2 \times 800}{320}=10$