Two sirens situated one kilometer apart are producing sound of frequency 330 Hz. An observer starts moving from one siren to the other with a speed of 2 m/s. if the speed of sound be 330 m/s. What will be the beat frequency heard by the observer ?

Options

A. 8
B. 4
C. 6
D. 1

Answer

B

Explanation

Here `" " f_(1) = (330 - 2)/(330) xx 300`
= 328 Hz.
and `" " f_(2) = (330 + 2)/(330) xx 330` = 332 Hz
Beat freq. = 332 - 328 = `4s^(-1)` .
correct choice is (b) .