A car traveling at 21.7 m/s honks its horn as it directly approaches the side of the big building. The horn generates a long sustained note of frequency f0 = 249 Hz. The sound is reflected off the building back to the driver of car. The sound wave from the original note and that reflected off the building join to make a beat frequency. Determine the beat frequency which the driver hears (which tells him that he had better strike the brakes!)? Suppose the speed of sound in air is around 341 m/s.