Question

A source of sound is moving towards a stationary observer with one-ninth the speed of sound. Calculate the ratio of apparent to real frequency

Answer 1

The apparent frequency is

$$f'=f \frac{v}{v-v_a}$$

The ratio of apparent to real frequency:

$$\frac{f'}{f}= \frac{v}{v-v_a}=\frac{1}{1-\frac{v_a}{v}}$$

$$\frac{f'}{f}= \frac{1}{1-\frac{1}{9}}=\frac{9}{8}$$