>> A driver travels northbound on a highway at a speed of 23.0 m/s. A police car, traveling southbound at a speed of 42.0 m/s approaches with its siren sounding at a frequency of 2260 Hz. (a) What frequency does the driver observe first as the police car approaches and then as it passes? (b) Repeat part (a) for the case in which the police car is northbound. I got part (a) using the formula f'=f (v+vo)/(v-vo) and f'=f (v-vo)/(v+vo), but I don't understand how to do part (b). If the police car is northbound, it would still be approaching and passing the driver... wouldn't the formulas stay the same? >> A sound wave in air has a pressure amplitude equal to 3.94x10^-3 Pa. Calculate the displacement amplitude of the wave at a frequency of 10.3 kHz. (Note: In this section, use the following values as needed, unless otherwise specified. The equilibrium density of air is 1.20 kg/m^3; the speed of sound in air is v=343 m/s. Pressure variations are measured relative to atmospheric pressure, 1.013x10^5 Pa.) I'm really not even sure how to start this problem... any suggestions?