A police siren has a frequency of 550 Hz as the police car approaches you, and it is 450 Hz after it has passed and is moving away. What is the speed of the police car

To solve this problem we will apply the concepts related to the Doppler effect. The Doppler effect is the change in the perceived frequency of any wave movement when the emitter, or focus of waves, and the receiver, or observer, move relative to each other. The image ambulance moves from left to right.

Here,

v = Velocity of sound

= Frequency of approaching sound waves

= Frequency of falling sound wave

Replacing with our values we have,

Therefore the velocity is 34.3m/s

blue light is scattered in different directions by the tiny molecules of air. blue is scattered more than other colours because it has a shorter distance to travel which results in smaller waves. this is why we see a blue sky most of the time.