What happens to the amplitude change of a train that slows down and stops as it approaches?

Why does the amplitude change?
Isn’t the amplitude constant regardless of velocity or approaching direction?
Rather, since it has stopped, it seems to decrease to 0, so why is “increases” the answer?

It is due to the Doppler effect.
There are good descriptions of the Doppler effect on the net. If they do not suffice, let me know, if there are still questions.

We know that the Doppler effect changes the frequency and wavelength.
How is amplitude affected?

No wave is eternal in the atmosphere due to the resistance of the air molecules. This will absorbe the energy of the waves, thus their amplitude of their vibration decrease, the more it travels away from the source.
When the train comes closer to you, you will experience higher amplitudes, approaching the amplitudes just next to the source.

Oh, I didn’t notice “the sound heard by the person”.
Normally, the amplitude would not change, but since this person is experiencing increasingly louder sounds, the answer to this problem is “the amplitude increases,” right?
thank you so much

You’re welcome.
But the amplitude changes irrespective of whatever (as I described).
It does even change near the black holes or gravitational waves despite lack of air/atmosphere. (I am aware we do not have sound waves in the outer space, but generally electromagnetic waves I mean)

Theoretically on the paper, yes it does not change if we are in a hollow universe.

Yes, the amplitude increases for the person with an approaching train.

ah! I really understand now. Thank you!

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hi is this on the imat syllabus?

Period and frequency is in the syllabus.
So, I suppose it covers every kind of periodic movement.

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@user14 I had forgotten to answer your last question. This is why I made it clear by confirming what I described earlier and how I reached that conclusion. I am not sure whether you understood my argument since you have apparently found something funny in it which I don’t understand as well. Good luck with the IMAT 2023.