Answer:
5-B
8-B
18-C
Step-by-step explanation:
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The answers are
5- B- Forced vibrations, such as those that occur between a fretboard and a large cabinet surface, produce a much lower sound than that produced by the original vibrating body.
8- B. The area covered by the wavefront increases as the wave progresses, but the energy that passes through a wavefront in a unit of time decreases.
18- c- The frequency of the sound waves will change for the listener as a result of the Doppler effect.
The Doppler effect is a change in frequency due to a change in the source.