Kate was overworked; this is not passive voice since Kate was not acted upon. SV+ predicative adjective
The premises staff cleaned the floor. This is an active sentence where the verb is in past tense. SVO
The papers should be photocopied. This is a passive sentence: SV.
S = the papers = result (thing affected by the action); therefore, this sentence is passive.
Where the subject is the result and not the agent, you see a passive structure.
They should photocopy the papers. This is an active sentence.
SVO. S = they = agent, O = the papers = the result (thing
affected by the action)