A motor car is approaching towards a crossing with a velocity of 72 k m h - 1 . The frequency of the sound of its horn as heard by a policeman standing on the crossing is 260 Hz . The frequency of horn is

Question

A motor car is approaching towards a crossing with a velocity of 72 k m h - 1 . The frequency of the sound of its horn as heard by a policeman standing on the crossing is 260 Hz . The frequency of horn is, 200 Hz, 244 Hz, 150 Hz, 80 Hz

MARKS App · Accepted Answer

From Doppler's effect, perceived frequency is ν ′ = ν v - v o v - v s v s = 72 km h - 1 = 72 × 1000 60 × 60 = 20 m s - 1 v o = 0 , v = 332 m s - 1 , ν ′ = 260 Hz 260 = ν 332 332 - 20 ⟹ ν = 260 × 312 332 = 244 Hz

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