1. "in" is a preposition.
2. "in" is an adverb.
Prepositions always begin prepositional phrases which end with a noun or pronoun.
1. He got in the car.
(What is the part of speech of 'in'?)
2. Get in!
(What is the part of speech of 'in' here?)
2 answers
1. "in" is a preposition here
2. "get in" is considered a phrasal verb:
http://www.eslcafe.com/pv/pv-g.html
(scroll down a bit)
2. "get in" is considered a phrasal verb:
http://www.eslcafe.com/pv/pv-g.html
(scroll down a bit)