Asatellite in circular orbit around the earth moves at constant speed. this orbit is maintained by the force of gravity between the earth and the satellite, yet no work is done on the satellite. how is this possible?

a. no work is done if there is no contact between objects.
b. no work is done because there is no gravity in space.
c. no work is done if the direction of motion is perpendicular to the force.
d. no work is done if objects move in a circle.

C. No work is done if the direction of motion is perpendicular to the force.

Explanation:

We know that work is the dot product of force and displacement.

Let's take the angle between the force and the displacement = θ

W= F . d cosθ

F=Force  , d=Displacement  

If θ = 0° then W= F.d

If θ = 90° then W= 0

So we can say that when force is perpendicular to the displacement then the work done by force will be zero.

Therefore the answer is C.

the largest known star in the universe is uy scuti, a hypergiant with a radius around 1,700 times larger than the

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.