What processes occur when a meteor enters earth's atmosphere and then what will be speed of meteor when it encounters air resistance?
As an incoming meteoroid approaches the Earth, it encounters atmospheric atoms and molecules, some of which are absorbed and trapped in the meteoroid. The generated heat causes atoms to boil off and collide with those in the atmosphere. This produces ionized particles which surround the meteoroid with a glowing envelope leaving a column of plasma. The meteoroid is now seen as a meteor. If the meteor trail persists over a second, it’s called a train. Trains may last for many minutes, and can be used to observe upper atmosphere movements. Most meteoroids do not survive the entry process, but those that do are called meteorites.
Meteorites tend to travel at very fast speeds (around 11-70 km per second, according to this article., as a result of the atmosphere slowing them down, they heat up - forming the 'fireball' normally viewed as one enters the atmosphere, and some may explode in the sky (eg Tunguska and the recent Russian event).
For exceptionally large ones, the atmosphere may as well as not be there.