The maximum frequency recorded is 751 Hz and the minimum frequency recorded is 749 Hz. Explain this observation.

Determine the speed of the mosquito.

as the mosquito approaches the wavelength perceived by Georgia is shorter and therefore the perceived frequency is higher;

as the mosquito is moving away, the wavelength perceived is longer than the emitted and therefore the perceived frequency is lower;

due to the Doppler effect;

approaching $751 = f \times \frac{{340}}{{340 - u}}$;

moving away $749 = f \times \frac{{340}}{{340 + u}}$;

to produce $u = 0.45{\text{ m}}\,{{\text{s}}^{ - 1}}$;

or

emitted frequency is $\frac{{751 + 749}}{2} = 750{\text{ Hz}}$;

applying the Doppler effect for approach (or recession), $751 = 750\frac{{340}}{{340 - u}}$$\,\,\,$or$\,\,\,$$749 = 750\frac{{340}}{{340 + u}}$;

to produce $u = 0.45{\text{ m}}\,{{\text{s}}^{ - 1}}$;

In (a), many candidates drew the classic diagram with wavefronts closer in front of the source and further apart behind. However, very few related this to the situation and the values given.

(b) was a more difficult question with few working through to the solution.