Question

A source of sound S emitting frequency 100 Hz and an observer O are located at some distance from each other. The source is moving with a speed of 19.4 m s^-1 at an angle of 60° with the source observer line as shown in the figure. The observer is at rest. The apparent frequency observed by the observer (velocity of sound in air is 330m s^-1) is:

(a) 100 Hz

(b) 103 Hz

(c) 106 Hz

(d) 97 Hz

Answer 1

Correct option is : (b) 103 Hz

The apparent frequency heard by observer

\(f_o = f_s[\frac{v}{v - v_s \cos60^\circ}] = 100[\frac{330}{330 - 19.4\times\frac{1}{2}}]\)

\( = [\frac{330}{300 - 9.7}] = 100[\frac{300}{320.3}]\) 

= 103.02 Hz