Are both sentences OK?
(a rope, string, line etc)

Pull it as hard as you can.
Pull it as strong as you can.

Question

Are both sentences OK?
(a rope, string, line etc)

Pull it as hard as you can.
Pull it as strong as you can.

Answer

"Pull it as hard as you can" is correct. It means to pull with all your strength.

"Pull it as strong as you can" is incorrect but native speakers will understand what you mean.

Answer

Only 'hard' is right.