A pedestrian standing on the sidewalk hears the siren of an ambulance as it travels…
PHYSICS · Multi-part · AP · Physics 2: Algebra-based · Waves Sound and Physical Optics · Waves Sound and Physical Optics
Problem
A pedestrian standing on the sidewalk hears the siren of an ambulance as it travels in a straight line parallel to the curb. While the ambulance approaches, the pedestrian measures a steady frequency of 820 Hz; immediately after the ambulance passes, the measured frequency is 780 Hz. Air conditions are uniform and wind can be neglected.
(a) Write two mathematical relationships that connect the observed frequencies (820 Hz and 780 Hz) with the siren’s unknown rest frequency and the ambulance’s unknown speed.
(b) Solve the relationships from part (a) to determine the speed of the ambulance. Clearly state any algebraic steps taken.
(c) Using your result from part (b), determine the rest frequency of the ambulance siren.
(d) Explain, without additional calculation, whether the pedestrian would experience any change in the perceived loudness of the siren that is directly attributable to the Doppler effect, and justify your reasoning in terms of wave phenomena.