Page 466 - Practical English Usage 3ed - Michael Swan, Oxford

prepositions (5): at the ends of clauses 452 This is particularly common with the noun place.
We need a place to live (in). She had no place to go (to). For the use or prepositions after /lear, see 365.
452 prepositions (5): at the ends of clauses 1 introduction
A preposition often connects two things: (1) a noun, adjective or verb that comes before it, and (2) a 'prepositional object' - a noun phrase or pronoun that comes after the preposition.
This is a present for you. He's looking at her.
I'm really angry with Joe. TIley live in a small village.
In some structures we may put the prepositional object at or near the beginning of a clause. In this case, the preposition does not always go with it - it may stay together with 'its' noun, adjective or verb at the end of the clause. This happens especially in four cases:
wh-questions:
Who's the present for?
Joe's the person that I'm angry with. She likes to be looked at.
When a question word is the object of a preposition, the preposition most often comes at the end of the clause, especially in informal usage.
Who's the present for? (For whom is the present? is extremely formal.) What are you looking at?
Who did you go with?
Where did she buy it from?
Which flight is the general travelling on?
What kind offilms are you interested in?
This also happens in indirect wh-questions. and in other what-clauses.
Tell me what you're worried about.
What a lot oftrouble I'm in!
Some questions consist simply of question word + preposition. What with? Who for?
However. this structure is unusual when there is a noun with the question word.
With what money? (NOT Whaf merle,.' with'!) 3 relative clauses
When a relative pronoun (see 494) is the object of a preposition, the preposition also often goes at the end of the clause. especially in informal usage.
Joe's the person that I'm angry with. (Less formal than ... with whom I am angry.)
This is the house (that) I told you about.
(Less formal than ... about which I told you.)
You remember the boy (who) I was going out with?
relative structures:
passives:
infinitive structures: The village is pleasant to live in.
2 wh-questions
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