Question

I have a question of physics based math

Answer 1

Sound reflected by moving wall

Answer 2

The professor said that the red is more correct than green.
But why and how did he use those equations?
Can anyone explain?

Answer 3

https://en.wikipedia.org/wiki/Doppler_effect#General

Answer 4

Why not just watch his videos, he explains it all, actually he has a whole playlist:
https://www.youtube.com/watch?v=XeXZVge61S4
https://www.youtube.com/watch?v=l77-3Qv5X1o (yours)

But you can use either method, as the wall is moving.

Answer 5

my dear @Astrophysics
The 25th lecture is wrong!
Check for that he has made 25.5 lecture, next to this video
:D

Answer 6

And I wonder how these two have been used?
They are not equal, hence why we use them?

Answer 7

@PaxPolaris
Can you explain in terms of the wall.
Only the wall thing is creating problem.
Or you can give a link