An airplane travels at a speed of 0.5v where v is the speed of sound. The airplane approaches a stationary observer .The frequency of sound emitted by the aircraft is in 200Hz. Which frequency does the observer hear?
Correct answer: A. 400 HZ
- A. 400 HZ
- B. 100 HZ
- C. 120 HZ
- D. 180 HZ
Explanation
Given: Speed of sound = Vs = 340 ms-1 Speed of aeroplane = Va = 0.5 × 340 = 170 ms-1 Frequency = f = 200 Hz Frequency = f ' = ? Using the formula: f ' = Vs / (Vs - Va)× f = 340 / (340 - 170) × 200 = 340 / 170 × 200 = 2 × 200 f ' = 400 Hz
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About Waves
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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