Một ngƣời di chuyển một chiếc xe với vận tốc không đổi. Lúc đầu ngƣời ấy kéo xe về phía trƣớc, sau đó ngƣời đẩy
xe về phía sau.
Trong cả hai trƣờng hợp, càng xe hợp với mặt phẳng nằm ngang một góc α. Hỏi
trong trƣờng hợp nào ngƣời ấy phải đặt lên xe một lực lớn hơn? Biết trọng lƣợng của xe
là P, hệ số ma sát giữa bánh xe và mặt đƣờng là k.

c)as speed changes, wavelength and frequency change.

everything changes!

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.

a is the best answer your welcome

because if the tool that you are using is not balanced it there would be false mass.