Final answer:
The frequency of the approaching train's whistle is determined using the concept of beat frequency, which is the absolute difference between the frequencies of two sound sources. Given the beat frequency of 4.0 Hz, the actual frequency of the approaching train's whistle is 566 Hz.
Step-by-step explanation:
The question involves the concept of beat frequency, which arises when two sound waves with close frequencies are superimposed, leading to a phenomenon where the sound level fluctuates at a frequency equal to the absolute difference between the two frequencies. In this case, the stationary train conductor hears a beat frequency of 4.0 Hz when the other train approaches, and the whistle frequency of the stationary train is 570 Hz. The frequency heard by the stationary train conductor can either be the sum or the difference of the two whistle frequencies. Therefore, the frequency of the approaching train's whistle is either:
- 570 Hz - 4 Hz = 566 Hz
- 570 Hz + 4 Hz = 574 Hz
Since the approaching train is moving towards the conductor, the Doppler effect implies that the frequency heard by the stationary conductor will be higher than the actual frequency of the approaching train's whistle. Hence, the correct answer is 566 Hz, as the approaching train's frequency is lower, indicating it will increase to the beat frequency when heard by the stationary conductor.