Wave Mechanics Question 689
Question: A source of sound S emitting waves of frequency 100 Hz and an observer 0 are located at some distance from each other. The source is moving with a speed of $ 19.4m{{s}^{-1}} $ at an angle of $ 60{}^\circ $ with the source observer line as shown in the figure. .The observer is at rest. The apparent frequency observed by the observer is (velocity of sound in air $ 330m{{s}^{-1}} $ )
Options:
A) 103 Hz
B) 106 Hz
C) 97 Hz
D) 100 Hz
Show Answer
Answer:
Correct Answer: A
Solution:
[a] Here, original frequency of sound, $ f _{0}=100,Hz $ Speed of source $ V _{s}=19.4,\cos ,60{}^\circ =9.7 $ From Doppler’s formula $ f=f _{0}( \frac{V-V _{0}}{V-V _{s}} ) $
$ f=100( \frac{V-0}{V-(+9.7)} ) $
$ f=100\frac{V}{V( 1-\frac{9.7}{V} )}=\frac{100}{( 1-\frac{9.7}{330} )}=103,Hz $ Apparent frequency $ f=103,Hz $
BETA
