An elevator is constructed using an electric motor at the top which is used to lift the elevator's car via a cable. the cable weighs 6 pounds per foot. the cable is 100 feet long when the elevator car is at the first floor, and it is effectively 0 feet long when the car is at the top floor. the elevator's car weighs 500 pounds how much work w does the motor do just lifting the cable and car when it takes the car from the first floor to the top floor

80000 lb-ft

Explanation:

= Weight

h = Height

The work done by the car is

Weight of the cable is 6 pounds per feet

Total weight of cable

Work done to lift the cable

h = 50 as the CG will be center of the length of the cable

Total work done by the motor will be the sum of the work done

The work done to lift the car and motor is 80000 lb-ft

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.