A vehicle is moving with a speed of $$\(30.0 \mathrm{~m} \mathrm{~s}^{-1}\)$$ directly towards a stationary observer. The horn of the vehicle emits sound of frequency 440 Hz . The speed of sound in air is $$\(340 \mathrm{~m} \mathrm{~s}^{-1}\)$$.
A.
B.
C.
D.
Exam No：9702_s25_qp_14 Year：2025 Question No：22
Answer:
D
Knowledge points:
7.3.1 understand that when a source of waves moves relative to a stationary observer, there is a change in observed frequency
7.3.2 use the expression for the observed frequency when a source of sound waves moves relative to a stationary observer
7.3.3 appreciate that Doppler shift is observed with all waves, including sound and light
Solution:
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