2) a 5 lb force pulls at an angle of 25º, as measured counterclockwise from the +x axis, on a
box having a mass of 7 kilograms. the box is on a horizontal surface and the coefficient of
friction between the box and the surface is 0.20. determine the following:
a) what is the mass of the box expressed in slugs ?
b) what is the weight of the box, expressed in pounds?
c) what is the magnitude of the normal force acting on the box?
d) what is the magnitude of the frictional force acting on the box?
e) what is the net force acting along the line of motion acting on the box?
f) what is the acceleration of the box, expressed in ft/s? ?
g) if the box starts at rest, and the forces act throughout the motion, calculate how far
the object travels in 3 seconds. express the answer in feet.
h) if the box starts at rest, and the forces act throughout the motion, calculate how fast
the box is travelling at 3 seconds. express the answer in ft/sec
i) what is the kinetic energy of the box at 3 seconds (again, the forces act throughout
the motion)? express your answer in both ft lbs.

it doesn't. it was imagined up in the middle ages.

-4 on

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.