A police car, traveling at 60 miles/hr, passes an innocent bystander while sounding its siren, which has a frequency of 2000 Hz. What is the overall change in frequency of the siren as heard by the bystander?
The police car continues down the street, the far end of which is blocked by a high brick wall. What does the bystander hear when the acoustic reflections from the wall are superimposed on the sound coming directly from the siren?