Q. Two whistles $A$ and $B$ produce notes of frequencies $660\ Hz$ and $596\ Hz$ respectively. There is a listener at the mid-point of the line joining them. Now the whistle $B$ and the listener start moving with speed $30\ m/s$ away from the whistle $A.$ If speed of sound be $330\ m/s,$ how many beats will be heard by the listener
A) 2
B) 4
C) 6
D) 8
Explanation
(b) For observer note of $B$ will not change due to zero relative motion.
Observed frequency of sound produced by $A$
$= 660\frac{(330 - 30)}{330} = 600\ Hz$
$\therefore$ No. of beats $= 600 - 596 = 4$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.