Wave Motion 4 Question 9

9. A police car with a siren of frequency 8kHz is moving with uniform velocity 36km/h towards a tall building which reflects the sound waves. The speed of sound in air is 320m/s. The frequency of the siren heard by the car driver is

(a) 8.50kHz

(b) 8.25kHz

(c) 7.75kHz

(d) 7.50kHz

(2011)

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Answer:

Correct Answer: 9. (a)

Solution:

  1. 36km/h=36×518=10m/s

Apparent frequency of sound heard by car driver (observer) reflected from the building will be

Correct option is (a).



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