Why would it be difficult to experimentally calculate the speed of sound in the classroom with a stopwatch and meter stick?

Sound travels quite fast and sound wave must pass through a medium, such as air.

To measure a sound in classroom you will require to measure the time it takes a sound to travel a measured distance using stopwatch and meter stick but it would be difficult because walls of classroom will create echos echos.

Echos are reflections of sounds which causes timing errors and make difficult to meausre the speed of sound.

layer a is the exosphere and layer b is the thermosphere.   is the answer i think but i hope this .

scattering of light by tiny particles in air to produce the colors we see on sky, is dependent on the following factors:

(i) wavelength of light

(ii) size of the scattering particle  

(iii) distance traveled by light through the atmosphere.

according to rayleigh's law of scattering, the amount of scattering is inversely proportional to the fourth power of its wavelength. shorter the wavelength, greater is its scattering. hence violet/blue light is scattered more than red.

sun's light is a composite light ( visible light) with wavelengths in the range 400 nm (violet) to 700 nm (red). as sunlight passes through our atmosphere, the molecules of air scatter light according to their wavelengths. during sunrise and sunset, the sun's position is below the horizon. hence light from the sun travels a greater distance in the atmosphere when compared to its position a noon.

as sunlight enters the earth's atmosphere, blue light is scattered away and at the end of its journey in the sky, only red and orange wavelengths remain in the beam.

hence at sunrise and sunset, the sky appears reddish orange.