The principle of momentum conservation states that if there no external force the total momentum of the system before and after the collision is conserved.
Since momentum is a vector, we should investigate the directions and magnitudes of initial and final momentum.
If the first ball hits the second ball with an angle, we should separate the x- and y-components of the momentum (or velocity), and apply conservation of momentum separately on x- and y-directions.
The skin in humans ranges from darkest to the lightest color, as a result of genetic makeup, exposure to the sun rays, skin pigmentation may be either due to the evolutionary process of natural selection, and it may be due to the biochemical effects of the UV rays.
As the pigment in the skin of humans is affected by the content of melanin in the body that causes the determination of skins cells of the darker colored humans, and the light skin is determined by the bluish-white tissues under the dermis and the hemoglobin.
The emergence of skin pigments dates back to 1.2 billion years ago. When the harsh climatic conditions drove the early humans into arid and open landscapes. In general, the people living near to equator have darkly pigmented than those living in poles are lightly pigmented.
