Question

a police car travels towards a stationary observer at a speed of 15 m/s . the siren on the car emits a sound of frequency 250 hz .calculate the recorded frequency .the speed of sound is 340 m/s
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Answer 1

2. $340 \div 340 - 15 \times 250$

Answer 2

Answer:1725.78 Hz

Explanation:

Given

$v_s=15 m/s$

Frequency f=250 Hz

Speed of sound v=343 m/s

According to Doppler effect an increase in frequency would be recorded as the source of sound moves towards the listener.

Apparent Frequency $f'=f\left [ \frac{1}{1-\frac{v_s}{v}}\right ]$

$f'=1600\times 1.078=1725.78 Hz$