A pedestrian standing on a quiet sidewalk hears an ambulance siren whose rest frequency is 950Hz. The ambulance moves in a straight line directly past the pedestrian at a constant speed of 18m/s. The speed of sound in air is 343m/s.
(a) Calculate the frequency heard by the pedestrian immediately before the ambulance reaches the point of closest approach.
(b) Calculate the frequency heard immediately after the ambulance has passed that point.
(c) The pedestrian is holding a 950Hz tuning fork. Determine the beat frequency heard just before and just after the ambulance passes.
(d) Describe qualitatively how the beat volume perceived by the pedestrian will change as the ambulance moves from approaching to receding.