Department of Pre-University Education, KarnatakaPUC Karnataka Science Class 11
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A Traffic Policeman Standing on a Road Sounds a Whistle Emitting the Main Frequency of 2.00 Khz. What Could Be the Apparent Frequency - Physics


A traffic policeman standing on a road sounds a whistle emitting the main frequency of 2.00 kHz. What could be the apparent frequency heard by a scooter-driver approaching the policeman at a speed of 36.0 km h−1? Speed of sound in air = 340 m s−1.

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Velocity of sound in air v = 340 ms−1
Velocity of scooter-driver \[v_o\]= 36 kmh−1 =

\[36 \times \frac{5}{18}   =   10   {\text { ms }}^{- 1}\]

Frequency of sound of whistle \[f_o\]= 2 kHz

Apparent frequency \[\left( f \right)\]  heard by the scooter-driver approaching the policeman is given by : 

\[f = \left( \frac{v + v_o}{v} \right) \times  f_o\]

\[f = \left( \frac{340 + 10}{340} \right) \times 2\] 

\[   = \frac{350 \times 2}{340}  \text { kHz }\] 

\[   =   2 . 06 \text{ kHz }\]

Concept: Wave Motion
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HC Verma Class 11, 12 Concepts of Physics 1
Chapter 16 Sound Waves
Q 62 | Page 356
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