On Fig. 5.1, put a cross (x) at one node position and another cross at one antinode position. Label the node N and the antinode A.
Demonstrate that the wavelength of the wave produced is $0.32\,\text{m}$. Justify your answer.
Calculate the frequency of the wave.
A source of sound waves with frequency $780\,\text{Hz}$ is mounted on a rotating platform. Its speed is $39\,\text{m s}^{-1}$. The speed of sound in air is $320\,\text{m s}^{-1}$. Calculate the maximum frequency of the sound detected by the observer.
At time $t = 0$, the observer receives the sound emitted by the source when it was at the position shown in Fig. 5.2. On Fig. 5.3, sketch how the detected frequency $f$ varies with $t$ for one complete rotation of the platform. No calculations are needed.