Question

A source of sound S emitting waves of frequency 100 Hz and an observer O are located at some distance from each other. The source is moving with a speed of $19.4m{s}^{-1}$ at an angle of ${60}^o$ 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 $330m{s}^{-1}$)

• A. $97Hz$
• B. $100Hz$
• C. $103Hz$
• D. $106Hz$

Answer 1

The correct option is C $103Hz$

The apparent frequency,

$f^{\prime }=\frac{v}{v-v_S\cos \theta }$

$f=\frac{330}{330-19.4\times 0.5}=103Hz$