Describe what is meant by the Doppler effect as it relates to sound.

An ambulance is travelling at a speed of 28.0 ms^–1 along a straight road. Its siren emits a continuous sound of frequency 520 Hz. The ambulance is approaching a stationary observer. The observer measures the frequency of the note to be 566 Hz. Determine the speed of sound.

observed/perceived change in pitch/frequency;
when there is relative motion between source and observer;

recognize that \(f' = \left[ {\frac{v}{{v - {u_{\rm{s}}}}}} \right]f\);
\(566 = \left[ {\frac{v}{{v - 28}}} \right]520\);
to give v=345(ms^-1) ;
Award [0] for use of the moving observer Doppler equation.
Award [2 max] for the use of +28 to give -345(ms^-1).
Otherwise award only the first marking point for substitution of the incorrect values in the correct equation.