Three cars, each sounding an identical horn of rest frequency f0, move relative to a stationary roadside microphone.
• Car A approaches the microphone at 30m/s.
• Car B moves directly away from the microphone at 15m/s.
• Car C travels at 40m/s along a path perpendicular to the line joining it and the microphone.
Which ranking correctly orders the observed frequencies at the microphone from highest to lowest?
(a) fC>fA>fB
(b) fA>fB>fC
(c) fA>fC>fB
(d) fB>fA>fC