Final answer:
The automobile is moving away from the radar device, as indicated by the lower frequency detected by the stationary radar, which is a result of the Doppler effect.
Step-by-step explanation:
If a police officer's stationary radar device indicates that the frequency of the radar wave reflected from an automobile is less than the frequency emitted by the radar device, it means that the automobile is moving away from the radar device.
This is an application of the Doppler effect, specifically its manifestation with electromagnetic waves such as radar. When an object is moving away from the source of such waves, the waves are stretched, resulting in a lower frequency detected by the receiver, known as a red shift in the context of light.
Conversely, if the object were moving towards the radar, the waves would be compressed, leading to a higher frequency (blue shift).The frequency of the radar wave reflected from an automobile being less than the frequency emitted by the radar device indicates that the automobile is moving away from the radar device.
This is because the Doppler effect causes a decrease in frequency when the source of the waves is moving away from the observer. In this case, the radar wave is being reflected back to the stationary police officer at a lower frequency, indicating that the automobile is moving away from the officer.