The Doppler Effect equation in general: where "s" represents the sound "SOURCE" ( fs is the intrinsic frequency of the sound source, vs is the SPEED of source relative to air); "o" represents the "OBSERVER" ( fo is the frequency heard by the observe, vo is the SPEED of observer relative to air). "v" is the speed of sound in air, v = 343 m/s Note: in the formula "v" represents the speed of sound in air. (In the figures the speed of the police car is labeled v. Don't mix them up.) The problem solving boils down to choosing a sign in the numerator and/or choosing a sign in the denomitor, as shown in: Part A - Case 1:the police car is behind you and moves toward you. Calculate the frequency of the siren heard by you. Note: if you use the wrong calculation, your answer may be close to the answer from the correct calculation. This difference is NOT caused by rounding. To screen out the WRONG Calculations, the accepted range is set to be narrow. Make sure you keep sufficient digits. Keep 2 digits after the decimal point, in Hz.

The Doppler effect in general Observer moving at speed v, (relative to medium) Source moving at speed v, (relative to medium) Frequency perceived by observer: V J}+-? To I, V: speed of sound in the l + 'Ss medium V Numerator: +\" if observer moves toward source (higher f,) '*_1f observer moves away from source (lower /,) Denominator: - if source moves toward observer (higher Oo \"+\" if source moves away from observer (lower /,) + + - The signs im the numerator and denominator areINDEPENDENT. , _) 4