Wave Motion 4 Question 9
9. A police car with a siren of frequency $8 kHz$ is moving with uniform velocity $36 km / h$ towards a tall building which reflects the sound waves. The speed of sound in air is $320 m / s$. The frequency of the siren heard by the car driver is
(a) $8.50 kHz$
(b) $8.25 kHz$
(c) $7.75 kHz$
(d) $7.50 kHz$
(2011)
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Answer:
Correct Answer: 9. (a)
Solution:
- $36 km / h=36 \times \frac{5}{18}=10 m / s$
Apparent frequency of sound heard by car driver (observer) reflected from the building will be
$\therefore$ Correct option is (a).
