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A car moving with a velocity of 36 km/hr crosses a siren of frequency 500 Hz.

A car moving with a velocity of 36 km/hr crosses a siren of frequency 500 Hz. The apparent frequency of siren after passing it will be

Options

(a) 520 Hz
(b) 485 Hz
(c) 540 Hz
(d) 460 Hz

Correct Answer:

485 Hz

Explanation:

Velocity of the car = 36000 m / 3600 s = 10 m/s
ʋemitted = 500 Hz, ʋsound = 330 m/s
ʋobs = ʋemitted [(ʋsound – ʋobs) / ʋsound]
Observed frequency ʋobs = 500 [(300 – 10) / 300]
⇒ ʋobs = 485 Hz

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