PHYSICS · Multi-part · AP · Physics 2: Algebra-based · Waves Sound and Physical Optics · Waves Sound and Physical Optics
Problem
An ambulance drives east along a straight, level road at a constant speed of 15m⋅s−1 while its siren emits a steady tone of rest frequency f0. Four pedestrians are located as follows when the ambulance is exactly opposite a town clock that serves as a position reference:
• Pedestrian D stands 30m north of the road, walking north at 1m⋅s−1.
• Pedestrian E stands on the road 50m east of the clock, jogging west (toward the clock) at 4m⋅s−1.
• Pedestrian F stands on the road 20m west of the clock, texting and thus stationary.
• Pedestrian G stands 40m south of the road, running northeast such that her velocity components are 3m⋅s−1 north and 4m⋅s−1 east.
Assume still air.
(a) For the instant described, rank the frequencies heard by pedestrians D, E, F, and G from highest to lowest. Indicate any ties.
(b) Provide a concise qualitative explanation for each placement in your ranking, explicitly referencing the component of each pedestrian’s velocity that is parallel to the ambulance’s motion.
(c) Suppose the ambulance’s driver abruptly slows to rest in front of the clock. Predict qualitatively how, if at all, the ranking in part (a) changes a moment after the vehicle stops. Explain your reasoning.