A stationary source of frequency 680 Hz and a stationary wall lie on opposite sides of an observer. The observer moves towards the wall at 10 m/s. The speed of sound is 340 m/s. If the beat frequency between the direct and reflected sounds is N Hz, find N.
Physics · Wave Motion · doppler effect
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Question

A stationary source of frequency 680 Hz and a stationary wall lie on opposite sides of an observer. The observer moves towards the wall at 10 m/s. The speed of sound is 340 m/s. If the beat frequency between the direct and reflected sounds is N Hz, find N.

Physics · Wave Motion · doppler effect

G1 Physics · Accepted Answer

The direct wave travels in the same direction as the observer. Therefore, f₁ = 680(340−10)/340 = 680×330/340 = 660 Hz. The reflected wave travels opposite to the observer. Thus, fᵣ = 680(340+10)/340 = 680×350/340 = 700 Hz. Hence, fᵦ = 700−660 = 40 Hz. Therefore, N = 40.