Fetching details from the dictionary...

tough; stiff; hard
inflexible; obstinate; stubborn
tired; worn out
「強い」 has another reading with different meanings.
このご飯はちょっとこわい。
This rice is a bit tough.
今日のご飯は少し強かった。
Today's rice was a bit tough.
この肉はそんなに強くない。
This meat isn't that tough.