The words whoa, woe sound the same but have different meanings and spellings. Why do whoa, woe sound the same even though they are completely different words?
The answer is simple: whoa, woe are homophones of the English language.
Used as a command to stop, as to a horse.
Deep distress or misery, as from grief; wretchedness. See Synonyms at regret.
Misfortune; calamity: economic and political woes.
Used to express sorrow or dismay.
Definitions from The American Heritage® Dictionary of the English Language, 4th Edition and Wordnik.
Homophones (literally "same sound") are usually defined as words that share the same pronunciation, regardless of how they are spelled.