Question 31: A source of sound moves towards a stationary observer with a speed one third that of sound. If the frequency of the sound from the source is 100 Hz, the apparent frequency of the sound heard by the observer is (Tag : Waves motion and sound sub-tag :
Correct answer: C. 150 Hz
- A. 67 Hz
- B. 100 Hz
- C. 150 Hz
- D. 75 Hz
Explanation
In this scenario, the observer is stationary (v₀ = 0), and the source is moving toward the observer with a speed of one-third the speed of sound (vs = -v/3). We are given that the frequency of the source (f₀) is 100 Hz. Therefore, the apparent frequency heard by the observer is 150 Hz
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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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