BMAT 2022 no19 Period and Frequency problem

Practice Question Solving
1

A train is travelling along a straight, horizontal section of track. The driver sees a maintenance worker ahead of the train on the track and so applies the brakes and the train decelerates. The driver also sounds a horn attached to the front of the train. The horn emits a note of constant pitch.
As the decelerating train approaches the worker, which of the following statements is/are correct?

  1. The pitch of the note heard by the worker is decreasing.

  2. The period of the sound wave heard by the worker is less than the period of the sound wave heard by the driver.

3.The sound wave approaches the worker at a speed that is decreasing.

A none of them
B 1 only
C 2 only
D 3 only
E 1 and 2 only
F 1 and 3 only
G 2and 3 only
H 1, 2 and 3

The answer is E.

What I don’t understand is period is inversely proportional to frequency.

The farther the distance, the lower the f so T should be bigger. Why is 2 correct?

2

From wikipedia: Compared to the emitted frequency, the received frequency is higher during the approach, identical at the instant of passing by, and lower during the recession.
The reason for the Doppler effect is that when the source of the waves is moving towards the observer, each successive wave is emitted from a position closer to the observer than the crest of the previous wave. Therefore, each wave takes slightly less time to reach the observer than the previous wave. Hence, the time between the arrivals of successive wave crests at the observer is reduced, causing an increase in the frequency.
→ TLDR: its bc of the increased frequency during the approach that the time period is smaller for the worker as compared to the driver.