So this is the sentence:
He is killed.
Okay here in this sentence "killed" is the adjective that modifies the subject and "is" is the linking verb. Now what about if I want to say this:
He is killed by a car.
Now here killed is still an adjective and "by a car" is an prepositional phrase which acts like an adverb ? Am I right ? And if yes then what happens after that now the full thing "killed by a car" is an adjective that modifies the subject ?
The first problem is that "he is killed" is hardly ever found in English: the only context I can imagine it is in a present-tense narrative, such as you find in some games. "He was/will be/has been/had been killed" are all fine.
Secondly, I don't agree that "killed" is an adjective here. It is part of the passive verb "be killed".
Thirdly, in general yes, some adjectives can take prepositional complements, and the whole phrase then behaves like an adjective. For example "attached" is an adjective which can take a "to" complement, but "attached to the wall" behaves in many way like an adjective.
I don't think it's helpful to regard the prepositional phrase as adverb-like, but you can if you like.
He is killed by a car
It is not natural in Present-day English to use "killed" as an adjective.
"Killed" is a past participle verb in the passive verb phrase "killed by a car".
The preposition phrase "by a car" is not a modifier, but a complement of the verb "killed".
In my experience, the prepositional phrase you are referring to is also an indirect object. Something that might help your sentence is to use the same tense throughout. "Killed" is past tense and "is" is present. For example: He was killed / he is dead. I hope this helps :)
