Can a 35cm bollard stop a truck?

Pneumatics. It'll have no problem.

Air gun type?

Air ram!

Haha time it right and punch it up through the floor of a car right as it drives over the bollard.

You know, there used to be things that you can buy to stop burglars:

Little spikes that you put under your seat... well I say "little" - they're a few feet long. As soon as someone sits on the seat activating the pressure pad on it, the spike punches up through the seat and, well, you get the picture. But, of course, there's a little code box thing that you enter a code into to turn the spike off. Therefor, a car theif who doesn't know the code, or that the spike is there will sit on the seat and BAM! Instant Kebab.

Holy fucking shit. That's intense.

Wow, so that's how you do it in Britain...

There was some british invention that has flamethrowers underneath the handles that one can activate if smeone is trying to enter their car

You can't beat British security systems.