John is pushing his daughter rachel in a wheelbarrow when it is stopped by a brick of height h (see figure below). the handles make an angle of ? with the ground. due to the weight of rachel and the wheelbarrow, a downward force mg is exerted at the center of the wheel, which has a radius r.
(a) what force f must john apply along the handles to just start the wheel over the brick? (use any variable or symbol stated above as necessary.)
(b) what are the components of the force that the brick exerts on the wheel just as the wheel begins to lift over the brick? in both parts, assume the brick remains fixed and does not slide along the ground. also assume the force applied by john is directed exactly toward the center of the wheel. (use any variable or symbol stated above as necessary.) (nx and ny components)

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.