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Sound frequency refers to the number of vibrations or oscillations of sound waves that occur in one second. It is measured in Hertz (Hz). Higher frequencies are perceived as higher pitches, while lower frequencies sound deeper. For the given exercise, the source emits sound at a frequency of 4000 Hz.
This frequency represents how many times a sound wave oscillates every second. Many musical notes and sounds we hear around us are categorized by their frequencies, which determine their perceived pitches.
In this particular exercise, understanding the emitted sound frequency is crucial, as it directly affects how the Doppler Effect influences what is heard by an observer. Recognizing the change or constancy in perceived sound frequency provides insights into movement characteristics of the sound source.

Source velocity refers to the speed of the sound source as it moves through space. In this exercise, the source moves at 22 m/s along the Y-axis.
The velocity of a source affects how its sound waves compress or spread out, influencing the frequency perceived by an observer. When a source approaches an observer, sound waves get compressed, raising the frequency and pitch; if the source moves away, the sound expands, lowering these attributes.
In this scenario, the source's velocity is crucial when applying the Doppler Effect. However, at the moment when the source is directly perpendicular to the observer (crossing the origin), its velocity component towards the observer becomes zero, resulting in no frequency shift at that instant.

Wave perception pertains to how sound waves are interpreted by an observer, which can be influenced by multiple factors like the relative motion of source and listener, and environmental conditions.
The Doppler Effect plays a key role in wave perception, where perceived sound frequency can change due to the movement of either the source or the listener. This effect mirrors real-world experiences like hearing a siren change pitch as it moves past you.
In the exercise, since the source crosses the origin perpendicularly, wave perception by the listener does not change. The perceived frequency is the same as the emitted frequency, 4000 Hz, as the motion has no impact along the listener's direction.

Speed of sound in air is a constant value, commonly taken as 330 m/s for calculations under typical conditions. This speed determines how quickly sound travels from the source to an observer, influencing how soon a sound is perceived.
Factors such as air temperature and pressure can slightly alter this speed, but in many calculations, like this exercise, it's considered constant to simplify the process.
In the given problem, the speed of sound is essential in applying the Doppler Effect formula correctly. Since there’s no velocity component change towards the listener at the instance of crossing the origin, the sound frequency remains unchanged, signifying the steady and predictable influence of sound speed on frequency calculations.