Part A.)Six boxes held at rest against identical walls. Rank the boxes on the basis of the magnitude of the normal force acting on them.

Rank from largest to smallest. To rank items as equivalent, overlap them.

1) 130N--->7kg

2) 150N--->1kg

3) 150N--->7kg

4) 120N--->3kg

5) 140N--->5kg

6) 140N--->3kg

(Since the boxes are at rest, Newton's 2nd law dictates that the horizontal forces on each box must add up to zero. You can use this information to determine the normal forces. If two boxes are both pushed against the wall by the same force, then they should experience the same normal force.)

Part B.) Rank the boxes on the basis of the frictional force acting on them.

Rank from largest to smallest. To rank items as equivalent, overlap them.

1) 130N--->7kg

2) 150N--->1kg

3) 150N--->7kg

4) 120N--->3kg

5) 140N--->5kg

6) 140N--->3kg

Explanation:

When a body is held against a vertical wall , to keep them in balanced position , normal force is applied on their surface . this force creates normal reaction which acts against the normal force and it is equal to the normal force as per newton's third law . Ultimately friction force is created which is proportional to normal force and it acts in vertically upward direction . It prevents the body from falling down .

Hence normal force = reaction force .

From second law also net force is zero , so if  normal force is N and reaction force is R

R - N = mass x acceleration = mass x 0 = 0

R = N .

Ranking normal force from  highest  to smallest

150 N , 130 N , 120 N

B )

Frictional force is equal to the weight of the body because the body is held at rest .

Ranking of frictional force form largest to smallest

7 kg , 5 kg , 3 kg , 1 kg .

Here frictional force is irrespective of the normal force acting on the body  because frictional force adjusts itself so that it becomes equal to weight in all cases here because it always balances the weight of the body .

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.