question_answer

Two factories are sounding their sirens at 800 Hz. A man goes from one factory to other at a speed of 2m/s. The velocity of sound is 320 m/s. The number of beats heard by the person in one second will be:     [JEE ONLINE 11-04-2014]

A)  2                                

B)  4         

C)  8                                

D)  10

Correct Answer: D

Solution :

[d] Given: Frequency of sound produced by siren, f = 800 Hz

Speed of observer,

Velocity of sound,

No. of beats heard per second = ?

No. of extra waves received by the observer per second

No. of beats/ sec