Final answer:
The car horn should be used in advance to provide a warning and ensure road safety. The specific timing can vary, but the principle is to allow enough time for others to react. The Doppler shift helps in recognizing the direction of an ambulance siren for appropriate action.
Step-by-step explanation:
The car horn should be sounded with sufficient warning to alert others and promote safety on the road. It serves as an auditory signal to indicate the presence of a potential hazard. The timeframe within which to sound the horn depends on the speed of travel and the situation on the road. For instance, if you are driving and see a woman with a baby stroller ahead, you should sound the horn well in advance to give her ample time to react and ensure her safety.
In the case of an emergency vehicle like an ambulance, the Doppler shift phenomenon is experienced, and drivers can detect the change in frequency of the siren as the vehicle approaches and passes by. This alert allows drivers to respond accordingly, typically by pulling over to allow the emergency vehicle through. The concept of Doppler shift helps distinguish the direction from which the siren is coming, with the highest frequency perceived when the ambulance is approaching, and a lower frequency after it passes.
Therefore, whether it's a car horn or an ambulance siren, timely use is essential for avoiding accidents and ensuring traffic safety.