A ball of mass 2.0 kg falls vertically downward. Just before hitting the floor its speed is 30 m/s. Just after rebounding upward its speed is 21 m/s. If this change in velocity took place in a time of 0.10 seconds, what is the average net force on the ball

The average net force on the ball is 1020 N.

Explanation:

Given that,

Mass of the ball, m = 2 kg

Its initial speed, u = 30 m/s

Just after rebounding upward its speed is 21 m/s, v = -21 m/s (direction is opposite of the initial direction)

If this change in velocity took place in a time of 0.10 seconds, t = 0.1 s

We need to find the net force on the ball. The net force is given by the product of mass and its acceleration as:

a is acceleration of the ball

So, the average net force on the ball is 1020 N. Hence, this is the required solution.

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.