A train moves with a driver with a speed of 90 km/h and produces a sound of 1000 Hz. The frequency heard by:
Correct answer: B. Less
- A. Same
- B. Less
- C. Greater
- D. Either (b) or (c)
Explanation
When the source of sound is moving towards the observer, the perceived frequency is higher (greater). However, if the source is moving away, the perceived frequency is lower (less). Since the train is moving away, the frequency heard by the observer is less than the emitted frequency.
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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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