Question

A source of sound of frequency $ 500 \,Hz $ is moving towards a stationary observer with velocity $ 30 \,m/s $ . The speed of sound is $ 330\, m/s $ . The frequency heard by the observer will be :

• A. $ 545 \,Hz $
• B. $ 580 \,Hz $
• C. $ 458.3 \,Hz $
• D. $ 550 \,Hz $

Answer 1

Answer: (D)

From Doppler's effect, the perceived frequency $\left(f'\right)$ is given by
$f'=f \frac{v}{v-v_{s}}$
where $v_{s}$ is velocity of source, $v$ the speed of sound and $f$ the original frequency. Given, $f=500\, Hz , v_{s}=30\, m / s , v=330 \,m / s$
$f'=500 \times \frac{330}{330-30} $
$f'=500 \times \frac{330}{300}=550 \,Hz$