>>7611080Let's say both comets are perfectly spherical.
The fire comet is cinnamon flavored, has a mass of exactly 1 megagram (one million grams), and a velocity of 100 km/s.
The ice comet is spearmint flavored, has a mass of 0.999999999999999... megagrams, and a velocity of 100 km/s traveling along a vector that coincides with the fire comet's vector but in the opposite direction.