A train has just completed a U-curve in a track which is a semicircle. The engine is at the forward end of the semicircular part of the track while the last carriage is at the rear end of the semi-circular track. The driver blows a whistle of a frequency of 200 Hz. The velocity of sound is 340 m/s. Then the apparent frequency as observed by a passenger in the middle of the train, when the speed of the train is 30 m/s is:
Correct answer: C. 200 Hz
- A. 219 Hz
- B. 288 Hz
- C. 200 Hz
- D. 181 Hz
Explanation
∴ There is no relative motion between the source and the observer, hence no change in real frequency is observed. Passenger(observer) is sitting inside the train emitting sound.
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Progressive waves transfer energy through oscillations, with wavelength, frequency, amplitude and wave speed related by v = fλ; sound speed depends on the medium. Superposition produces interference and stationary waves in strings and organ pipes, while simple harmonic motion describes the oscillation itself and must be distinguished from wave propagation.
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