The only time the past tense -ed ending is pronounced as a separate syllable “id” is when the verb ends in a “t” or “d” sound. Since “work” ends in a “k” sound, and does not end in a “t” or “d” sound, the past tense ending is not a separate syllable. The word “worked” is pronounced “workt”. When you try something and it’s effective, you say “it worked!”