A 20 kg block rests on a rough horizontal table. A rope is attached to the block and is pulled with a force of 80 N to the
left. As a result, the block accelerates at 2.5 m/s2. The
coefficient of kinetic friction uk between the block and the table
is

The coefficient of kinetic friction between the block and the table is 0.153

The given parameters;

mass of the block, m = 20 kg

force applied to the rope, F = 80 N

acceleration of the block, a = 2.5 m/s²

The coefficient of kinetic friction between the block and the table is calculated as;

where;

Fk is the frictional force

N is the normal reaction

The frictional force is calculated as follows

The normal reaction force is calculated as follows;

N = mg

N = 20 x 9.8

N = 196 N

The coefficient of kinetic friction between the block and the table is;

Thus, the coefficient of kinetic friction between the block and the table is 0.153

Learn more here: link

So we are applying 80 N on the block, 20kg in mass and it moves with the acceleration of 2.5 m/s/s

so we can find the force being applied on the block

F = ma

F = 20 X 2.5

F = 50 N

So only 50 N of the 80 N is being applied on the block.

Hence, the remaining 80-50 = 30 N force is being used to overcome friction

Force of Kinetic Friction = 30 N

Now, in this case the Normal Force will be equal to the Force applied by gravity(Mg)

So, Normal Force = 200 N

Coefficient of kinetic friction = Force of Kinetic Friction / Normal Force

Coefficient of kinetic friction = 30 / 200

Coefficient of Kinetic Friction = 0.15

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.

the rearrangement of particles in a physical change. hope this