1. The problem statement, all variables and given/known data Sally is a police officer who is standing in an intersection. A car driven by David approaches the intersection at a speed of 75 km/h. Sally blows her whistle (at a frequency of 900 hz) and signals the driver to stop. What does frequency does David hear? (speed of sound is 343 m/s). David does not stop and passes through the intersection and accelerates to 90 km/h, sally blows her whistle again, what frequency does David hear? 2. Relevant equations f'=(v-(v(D)-v(M)))/(v-(v(S)-v(M))*f 3. The attempt at a solution So the velocity of the median is zero, v is speed of sound =343 m/s , v(D) is David and at 75 km/h = 20.83 m/s and v(S) is sally = 0 and i also make it negative since travelling at sally so i go f'=(343-(-20.83))/343*900 = 954.65 Hz next I do the same as above except i make the v(D) = 90 km/h = 25 and is positive hence f'=(343-25)/343*900 = 834.40Hz this is my problem shouldn't the travelling away Doppler affect give a greater frequency than started with?