Kevin R. answered 07/20/15
Tutor
New to Wyzant
Love to learn, love to help others learn.
2 formulas for doppler shift frequency (well 8 actually)
1 for source moving toward stationary listener
Ft = [ v / (v - Vs) ] *f
1 for source moving away from listener
Fa = [ v / (v + Vs) ] *f
v is sped of sound -- 343 m/s
2Fa = Ft (frequency halved)
solve each for Vs (speed of car, source) , set 2 equations equal (Vs=Vs) f cancels
subsititute Ft = 2Fa
solve for Fa, then obtain Ft (1/2 fa).
answer is 1/3 of Vsound