Learn Russian: Почему грузовик тормозит?

Yes! It comes from the noun тормоз (a brake). Тормозить means to brake or to slow down. It is a regular second conjugation (И-type) verb, which is why it takes the -ит ending for the third-person singular form.

Can I use тормозить for things other than vehicles?

Yes, it has a very common everyday meaning. If a person is being slow to understand something, or if a computer or phone is lagging, Russians often say it тормозит (it is lagging or being slow).

How can I easily remember the word грузовик (truck)?

Look at its root: груз means cargo or a load. So a грузовик is literally a cargo vehicle. You will also see this root in related words like грузить (to load) and грузовой (cargo, used as an adjective).