The parking brake on a 1000 kg cadillac has failed, and it is rolling slowly, at 5 mph , toward a group of small children. seeing the situation, you realize you have just enough time to drive your 2000 kg volkswagen head-on into the cadillac and save the children. part a with what speed should you impact the cadillac to bring it to a halt?

To solve this problem we will apply the concepts related to the conservation of the Momentum. The initial momentum must be equal to the final momentum. Momentum is described as the product between body mass and its respective velocity. Since there is no movement at the end of the collision, the final momentum will be zero.

Our values are given as

Mass of Cadillac

mass of VW

Let VW impact with speed v, then for conservation of momentum

the Final speed is zero

Replacing,

Therefore the speed to bring the cadillac to a halt is 2.5mph

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.