Department of Pre-University Education, KarnatakaPUC Karnataka Science Class 11

# 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

Sum

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.

#### Solution

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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#### APPEARS IN

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