Final answer:
According to TC 545.251, an operator must stop at a railroad crossing if a signal from an engine is audible from 1,500 feet away, which is not one of the provided options. Using physics and the Doppler Effect, the change in frequency of a train horn can help determine the train's speed. An increase in sound intensity level by 30 dB in a community is significant and could be a cause for concern.
Step-by-step explanation:
According to TC 545.251, an operator approaching a railroad grade crossing must stop if a railroad engine approaching approximately 1,500 feet of the highway crossing emits a signal audible from that distance. Since none of the provided options (100, 200, 300, or 400 feet) are correct, it seems there might be a discrepancy. However, if we are looking at the different scenarios presented through the various physics problems, using the speed of sound and changes in frequency (Doppler Effect), we can analyze the movements of trains and the sound frequencies involved.
For example, if a commuter train blows a 200-Hz horn as it approaches a crossing and the speed of sound is 335 m/s, an observer will receive a different frequency while the train approaches and as it moves away due to the Doppler Effect. The actual speed of the train can be computed using the observed frequency and the known speed of sound. Similarly, a stationary person hears a different frequency based on whether the train is approaching or receding.
When it comes to sound intensity levels, an increase of 30 dB is significant as the decibel scale is logarithmic. An increase from 70 dB to 100 dB represents a considerable increase in sound intensity that could be bothersome and potentially harmful to the residents, thus the townspeople should be concerned.