A sound source moves in a large circle at speed 20 m/s. A stationary observer is very far away, and the speed of sound is 340 m/s. If fₘₐₓ/fₘᵢₙ = N/8, find N.
Physics · Wave Motion · doppler effect
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Question

A sound source moves in a large circle at speed 20 m/s. A stationary observer is very far away, and the speed of sound is 340 m/s. If fₘₐₓ/fₘᵢₙ = N/8, find N.

G1 Physics · Accepted Answer

For a far-away observer, fₘₐₓ = f×v/(v−u), fₘᵢₙ = f×v/(v+u). Therefore, fₘₐₓ/fₘᵢₙ = (v+u)/(v−u) = (340+20)/(340−20) = 360/320 = 9/8. Thus, N = 9.