Apolice car go goes flying past you on the highway with its sirens blaring. you notice as the police car gets closer, the pitch of the sirens changes. once the car passes you, the pitch begins to change again. what is happening? how does the doppler effect explain this phenomenon. answer in at least 3 sentences.

The change in pitch noticed here is known as the Doppler effect. The Doppler effect occurs when there is movement between the origin of a sound and its receiver. The point of origin of the sound or the receiver must move relative to each other. whenever the siren sends out a wave the car also moves forward in the same direction. This causes the sound waves to be pushed together. As the car moves away its is now travelling in the opposite direction and thus the wave are spread out more causing the pitch to lower. 

Divide 108.2 x 10^6 into 1.5 x 10 and the result will be in au (astronomical units)