Prepositions at the end

Hello.
I'd like to know what is the function of the prepositions in these sentences. Why do you need it? How can they be rephrased for a better understanding?
I use this knife to slice vegetables with.
Are you being attended to?
The bank was robbed and the safes were broken into.

They don't seem to be part of the pattern of a relative clause like this:
He is the man she works with. > He is the man with whom she works.

American English has many phrasal verbs or verbs with preposition. Therefore, we have slice with, attend to, and break into.

Slice with is not a true phrasal verb since “with” is an optional preposition.

We use the knife to slice the bread => We use the knife to slice the bread with => is rather redundant.

However, “with what do you slice the bread?” or “what do you slice the bread with?”

On the other hand, “attend” and “attend to” have different meanings

I attend school during the day, and attend to my sick brother in the evenings.

Similarly, “break” and “break into” have different meanings.

My sister broke the glass vase by accident, and immediately broke into tears.