(II) How much work did the movers do (horizontally) pushing a 46.0-kg crate 10.3 m across a rough floor without acceleration, if the effective coefficient of friction was 0.50?

2324 J

Explanation:

The formula for work is:

where is the force applied, and is the distance moved, in this case

and we need to find

Since the crate is not moving up or down, we conclude that the normal force must be equal to the weight of the object:

where is the normal force and is the weight, which is: , where g is the gravitational acceleration and is the mass .

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Thus the normal force is:

Now, the force due to the friction is defined as:

where is the coefficient of friction,

So, for the crate to move, the force applied must be equal to the frictional force:

And now that we know the force we can calculate the work:

substituting known values:

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.