Moving Source, Observer at Rest, derivation for Doppler effect

[ChiralSuperfields]

Homework Statement

Please see below

Relevant Equations

Please see below

For this,

Does someone please know whether they assume for the equation highlighted that $\frac{v}{f} ≥ \frac{v_S}{f}$ since otherwise the wavelength would be negative (which I assume is impossible)?

Many thanks!

 

[Frabjous]

Homework Statement: Please see below
Relevant Equations: Please see below

For this,
View attachment 327342
Does someone please know whether they assume for the equation highlighted that $\frac{v}{f} ≥ \frac{v_S}{f}$ since otherwise the wavelength would be negative (which I assume is impossible)?

Many thanks!

The object would be moving faster than the sound speed; i.e., supersonic which is a different physical regime.

 

[ChiralSuperfields]

The object would be moving faster than the sound speed; i.e., supersonic which is a different physical regime.

Thank you for your reply @Frabjous!