The siren of a fire engine that is driving northward at 31.0 m/s emits a sound of frequency 2020 Hz. A truck in front of this fire engine is moving northward at 19.0 m/s. a) What is the frequency of the siren's sound that the fire engine's driver hears reflected from the back of the truck?
b) What wavelength would this driver measure for these reflected sound waves?

A. Using

Fl= ( v+vl/v+vz)fz

= (340+19/340+31) x 2020

= 1954.7Hz

Then to find the frequency of sound when reflected from the truck such that the driver becomes the listener

we use

F"= ( v+vz/v+vl) fz

= 340+31/340+19 x 2020

2087.5Hz

B to find the wavelength of sound we use

Wavelength= V+vl/ F"

= 340+31/2087.5= 0.18m

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.