Ablock of mass m begins at rest at the top of a ramp at elevation h with whatever pe is associated with that height.

The PE associated with that height is given as, m×g×h

Explanation:

Potential energy (PE) is the energy possessed by an object when at rest. Its opposite is the kinetic energy (KE). When an object is at a certain height, it would possess potential energy because initially it is at rest. Also the value of the energy is determined by its mass, height and the force of gravity acting on it at that height.

So, the potential energy (PE) = mass× height× value of the gravitational force

                                                = m× g× h

Its unit is Joules. The potential energy of the mass would be converted to kinetic energy when it is in motion.

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.