You are trying to push a 30 kg canoe across a beach to get it to a lake. Initially, the canoe is at rest, and you exert a force over a distance of 3 m until it has a speed of 1.2 m/s.

a. How much work was done on the canoe?

b. The coefficient of kinetic friction between the canoe and the beach is 0.2. How much work was done by friction on the canoe?

c. How much work did you perform on the canoe?

d. What force did you apply to the canoe?

m = 30, g = 9.8, coefficient = 0.2, so force due to friction = 30 x 9.8 x 0.2 = 58.8 N, so work done by friction = 58.8 x 1.2 = 70.56 J

Explanation:

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.