"cow" represents one single syllable, with a diphthong: the first sound is AH and the second is the semivowel correspondent to OO. This sound is spelled in a lot of languages as au, as in Laura.
In IPA your guess is [kawri].
"kah-oh" represents two syllables: the first with the sound AH and the second with the vowel OH.
In IPA this is [kaori]. Very different.
You don't distinguish these two different sounds ("Whatever. Same thing.", your words), but that is your problem because in a lot of languages the difference between them is distinctive and it is important.
Again: if you don't know the right answer, don't reply.