Can we ask questions that we already know the answer when it seems to be a good question to the community? I am asking this because i think the reason this community is week and beta is that there is not much questions because some people is just answering because there is nothing they don't know to ask here. So if we ask a few healthy question that we already know the answer,wouldn't it be good?
Yes, you can do that. You can even answer your own questions immediately. In fact, when you write a question, there is a checkbox below the form that says,
Answer your own question – share your knowledge, Q&A-style
When you click that check box, a textbox for the answer will become visible, so you can submit your question and your answer in one step.
For more details, see Can I answer my own questions, even if I knew the answer before asking? on Meta Stack Exchange.
As Christopher says, you can ask questions and answer them yourself - that's a good way to build our knowledge base.
If you want to encourage community-building, you could also ask a question that you feel you know the answer to, but hold off on answering to allow some other users to contribute an answer.
Both of these would boost our Questions per Day statistics, which are currently the weakest part of our profile.
It's definitely good to check that the question is on-topic and also double-check that similar answers don't exist already on other similar questions.