Question

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

(a) 106 Hz

(b) 97 Hz

(c) 100 Hz

(d) 103 Hz

Answer 1

Correct option (d) 103 Hz

Explanation :

Here, Frequency of source, v₀ = 100 Hz

Velocity of source, v_s = 19.4 m/s 

Velocity of sound in air, v = 330 m/s 

As the velocity of source along the source observer line is v_scos60° and the observer is at rest, so the apparent frequency observed by the observer is