Question

There are 5 successive compressions of a sound wave train in a distance of 7.2 cm. If
the sound wave can travel 6.8 km in 20 seconds, determine the source frequency (in kHz).

Answer 1

First, find the wavelength:

$$\lambda=\frac{L}{N}=\frac{7.2}{5}=1.44\text{ cm}.$$

Second, calculate wave velocity:

$$v=\frac{d}{t}=\frac{6800}{20}=340\text{ m/s}.$$

The frequency is

$$f=\frac{v}{\lambda}=\frac{340}{0.0144}=23611\text{ Hz},$$

or 23.6 kHz.