Atrain, x meters long, traveling at a constant speed, takes 20 seconds from the time it first enters a tunnel 300 meters long until the time it completely emerges from the tunnel. one of the stationary ceiling lights in the tunnel is directly above the train for 10 seconds. find x

As the train is traveling at a constant speed, therefore the ratio of distance to time will be the same over any distance and respective time interval.

The train travels   m in 20 s.

As the stationary ceiling lights in the tunnel is directly above the train for 10 s, it means the train travels x m in 10 s, so in 20 s train travels 2 x m.

Therefore,

Hence, the length of the train is 300 m.

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.

causes

fossil fuels burn

cities become more industrialized

human population grows worldwide