Pronunciation - 갔

Pronunciation - 갔

New learner here (a couple of months of a few minutes a day regularly), I don't know any words, still trying to get my head around the alphabet and pronunciations.

I'm coming stuck on getting this to make sense in my head.

The word 갔, in my head, should be pronounced something similar to how we would pronounce 'kas' in English, albeit with different emphasis on the 's' sound.

But duolingo is pronouncing it more like 'car' or 'cara', which I'd expect to see as 갈 in Korean. Google translate almost pronounces it like 'can'.

Anyone able to explain how this should be pronounced, and why it isn't what I'd think?