Compared to the force needed to start sliding a crate across a rough level floor, the force needed to keep sliding once it is moving is 1) less 2) greater 3) the same

The force to start sliding a crate across a rough level uses the equation:

The force to keep it moving is given by:

Notice that N or the Normal Force stays constant because it's the same object throughout the experiment and angle of the ground is also constant. Therefore, only thing that makes a differences are the static and dynamic coefficients of friction. The comparison between them is given by the law:

Therefore, the force needed to start sliding a crate across a rough level floor is greater than the force needed to keep it sliding once it is moving. So, your answer is 2.

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Greater

Explanation:

As we know that when an object is placed on a rough floor then minimum force required to slide the object on the rough surface is known as limiting friction force.

Limiting friction is the maximum value of static friction between the object and ground surface.

So it is given as

Once the object start sliding on the rough surface then the friction force on the object is known as kinetic friction which is given by

now we know that

So it requires less force to move an object on rough floor once it starts sliding

So the force required to start sliding is greater than the force to move it once it start sliding

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.

weight of the box is given as

here this is placed on the inclined of angle 42 degree

now this weight will have two components one is along the incline other is perpendicular to it

so here we need to apply a force parallel to incline opposite to its component of weight

so here the component of weight is given as

here we have

so it requires 75 n force to move it upwards