Answer: 475 Hz.
- A 485 Hz
- B 477 Hz
- C 483 Hz
- D 475 Hz
Correct answer: D. 475 Hz
Explanation: Filing removes mass and raises a fork frequency. Since the beat rate fell (5 to 3), the fork moved closer to 480 Hz, so it started below it: 480 - 5 = 475 Hz.
A standing wave forms from two identical waves travelling in opposite directions and interfering; nodes (always zero displacement) and antinodes (maximum displacement) stay fixed in place, unlike a travelling wave where the whole pattern moves.
Concept context
Wave types, superposition, standing waves, Doppler effect, and sound intensity.