No: esți is singular, puternici is plural.
What is Du? I haven't met it in Romanian - do you mean Tu?
DL does also accept the singular version but it took me 3 goes to be consistent and not make mistakes like putting 'ti esți slab'!
How do I know that the sentence is plural or singular? English does not make that difference? You might want to add some clues to distinguish the form you want us to use or give the two options.