It would be a spectacular sight, but no one has ever observed it happening. I think if you apply the current definition of planet to the bodies involved, you could demonstrate that if two 'planets' collide then at least one of them is not a planet.
Huge and violent explosion, turning both planets basically into one volcanic planet/object. If there is some sort of life on any of it, well, after that, there won't be.
Asteroids are big rocks. When big rocks collide, the result is a lot of smaller rocks. It will look a LOT like this link, below.
no
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it makes an Earthquake
Asteriods are composed of rock that broke off of other planets.
When two continental plates collide they buckle up and fold forming mountains.
The molecules collide less frequently, which normally coincides with a decrease in temperature.
they hug each other
An earthquake happens.
If 2 tornadoes collide they will merge into one tornado.
an earthquake
it makes an Earthquake
when continents collide you bum your pet hamster
Asteriods are composed of rock that broke off of other planets.
A collision.
mountains are formed
mountains
Earthquakes and mountain building.
it makes a mountain
a big explosion occors