An observer standing on a railway crossing receives frequency of 2 . 2 kHz and 1 . 8 kHz when the train approaches and recedes from the observer. Find the velocity (in m s - 1 ) of the train. (The speed of the sound in air is 300 m s - 1 .)

Question

An observer standing on a railway crossing receives frequency of 2 . 2 kHz and 1 . 8 kHz when the train approaches and recedes from the observer. Find the velocity (in m s - 1 ) of the train. (The speed of the sound in air is 300 m s - 1 .),

MARKS App · Accepted Answer

f 1 = f 0 ( V ± V 0 ) ( V ∓ V S ) = f 0 v V ∓ V S W h e n a p p r o a c h e s : 2.2 × 10 3 = f 0 300 300 - V s ...(i) W h e n r e c e d e s : 1.8 × 10 3 = f 0 300 300 + V s ...(ii) Dividing (i) by (ii) 2 . 2 1 . 8 = 3 0 0 + V S 3 0 0 - V S ⇒ 4 0 . 4 = 6 0 0 2 V S ⇒ V S = 30 m s - 1

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