A train moving at a speed of 220 m s⁻¹ towards a stationary object emits a sound of frequency 1000 Hz. Some of the sound reaching the object gets reflected back to the train as echo. The frequency of the echo as detected by the driver of the train is (speed of sound in air is 330 m s⁻¹)

Question

Dr. Abubacker · Accepted Answer

[Solution from source] The object receives f₁ = f·v/(v − u) and reflects it; the moving driver then hears f₂ = f₁(v + u)/v = f(v + u)/(v − u) = 1000 × 550/110 = 5000 Hz. Treating only one Doppler shift gives 3000 Hz, which is wrong. Answer (3).

Q. A train moving at a speed of 220 m s⁻¹ towards a stationary object emits a sound of frequency 1000 Hz. Some of the sound reaching the object gets reflected back to the train as echo. The frequency of the echo as detected by the driver of the train is (speed of sound in air is 330 m s⁻¹)

Explanation

Reviewed by Dr. Abubacker

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