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Mr Marjanovic wrote (> sign from my original letter):
"> Collision types
> 1. Elastic: The difference of the sum of the kinetic energy of objects
> before and after the collision is zero.
> 2. Inelastic: A part of the sum of the kinetic energy converts to other
> form of energy during the collision.
> 2.1. Perfect inelastic: Velocities of objects are equal after the
> therefore objects are moving together.
> You have it that this is happened when an extraterrestrial object collided
> with Earth.
> What is the proof? Why didn't fly away a part or the whole object with
You have forgotten gravity. It is easy to calculate that almost the entire
ejecta of the impact fell back to Earth within hours. In other words: The
impact was in the short run a normal inelastic collision, and in the long
run a perfect inelastic collision."
I counted the energy balance of the collision that is your "short run"
time. From this viewpoint has two variants: The object (or part) stopped
or flew away.
If the object stopped then the object loss the whole kinetic energy. (This
is the perfect inelastic collision in this case.) If it flew away then a
part of the kinetic energy remaind at the object. (And after fall back to
Earth or if it has enough velocity then isn't fall back.)