The use of Doppler radar in the enforcement of traffic law has become common in the United States and many parts of the world. A typical “radar gun” (Fig. P23.58) emits a 24-GHz beam. A highway patrol officer aims the beam at a bus on the highway.
(a) If the reflected wave is 4.5 kHz higher in frequency than the emitted beam, how fast is the bus traveling in units of meters per second and miles per hour?
(b) Is the bus approaching or moving away? Hint: Here there are two Doppler shifts to the emitted beam. One shift occurs because the wave incident on the moving bus (the frequency “seen” by an observer riding on the bus) is Doppler shifted, just as if the bus were stationary with the radar gun approaching. A second Doppler shift occurs for the beam reflected off the moving bus because the bus acts as a moving source that radiates the frequency it “sees.” 

Transcribed Image Text:

Figure P23.58 Ses08