Question: For the following sentences:

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> * He threw the book *at* the floor.
> * He threw the book *on* the floor.
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> 
> 

I know the book hit the floor in both sentences but which one is more commonly used and also what's the difference between 'at' and 'on'? Do we acknowledge the exact position from 'at'?

Answer: 
I believe the word "on" also implies a final resting place. If you throw your book on the floor, and don't implicitly tell us where it ended up, we will immediately assume it's still on the floor. Similarly, if I "throw my clothes at the floor" on my way to the shower, it implies that I really don't care where they landed; they may have ended up on the back of a chair or on the dog laying in the corner. The emphasis is on that shower.
"Throw something on the floor" is usually used in more of an expressive than literal context. Usually, when you "throw something on the floor", you're not actually throwing it, you're dropping it casually, or maybe tossing it. Sometimes we might also use the expression to indicate we did something quickly: I threw on some clothes, throw dinner on the stove, etc. This does not mean that "throw on the floor" is never used literally ("during his tantrum, he threw all his food on the floor"). However, throwing at is generally used in a more literal sense, and usually indicates deliberateness and/or force.