A woman is sitting at a bus stop when an ambulance with a siren wailing at 430 Hz approaches at 31.0 m/s (about 69 mph). Assume the speed of sound to be 343 m/s. (a)
What frequency (in Hz) does the woman hear?
fa = Hz
With what speed vs (in m/s) would the ambulance have to travel in order for the woman to hear the siren at an apparent frequency of fa = 451 Hz?
vs = m/s

What frequency (in Hz) would the woman hear if the siren moved away from her with the same speed you found in part (b)?
fa = Hz