Hi, I've got a problem that I can't seem to find an explanation to, about the Doppler Effect An ambulance is going down the road at a speed U meters/second, in the same direction as the wind, which has a speed of W meters/second. The speed of sound in air is c meters/second Now, I have to choose one of three options: 1) always c>U+W 2) always c<U+W 3) neither (1) nor (2) At first I thought that the correct answer was (3), because I couldn't think of a reason why there should be a restriction to the speed of sound in air. The correct answer is (1) though, and I can't understand why. Can someone please enlighten me? Thanks for the help.