The words racked, wracked sound the same but have different meanings and spellings. Why do racked, wracked sound the same even though they are completely different words?
The answer is simple: racked, wracked are homophones of the English language.
Simple past tense and past participle of rack.
Simple past tense and past participle of wrack.
Definitions from Wiktionary, Creative Commons Attribution/Share-Alike License and Wordnik.
Homophones (literally "same sound") are usually defined as words that share the same pronunciation, regardless of how they are spelled.
If they are spelled the same then they are also homographs (and homonyms); if they are spelled differently then they are also heterographs (literally "different writing").