Passive formation applies to other persons as well as the basic فَعَلَ → فُعِلَ. The person/number suffix stays, while stem vowels become passive.
Word / formMeaning / explanation
ضَرَبْتَ → ضُرِبْتَyou (male) struck → you were struck.
ضَرَبْتِ → ضُرِبْتِyou (female) struck → you were struck.
ضَرَبْتُ → ضُرِبْتُI struck → I was struck.
ضَرَبُوا → ضُرِبُواthey (men) struck → they were struck.
ضَرَبْنَا → ضُرِبْنَاwe struck → we were struck.
For example, ضَرَبْتُ retains its first-person suffix ـتُ in ضُرِبْتُ; the vowel change inside the verb marks the passive.