Question

A source of sound producing wavelength 50 cm is moving away from a stationary observer with $\left( \frac{1}{5} \right)^{th}$ speed of sound. Then what is the wavelength of sound received by the observer?

• A. 55 cm
• B. 40 cm
• C. 60 cm
• D. 70 cm

Answer 1

Answer: (B)

40 cm

Answer 2

Here, wavelength of the source, $\lambda$ = 50 cm

Speed of the sound = v

Speed of the source, $v_{s} = \frac{1}{5}v$

As the source is moving away from the stationary observer, therefore the wavelength of sound received by the observer is

$\lambda' = \frac{(v + v_{s})}{v}\lambda = \frac{\left( v + \frac{1}{5}v \right)}{v}\lambda$

$= \frac{6}{5}\lambda = \frac{6}{5} \times 50cm = 60cm$