A detailed explanation of what is and is not a homework (or homework-like) question, and how to ask one, is available on this meta thread; what follows is a short summary.
What is considered a homework question here?
A "homework question" is any question whose value lies in helping you understand the method by which the question can be solved, rather than getting the answer itself. This includes not just questions from actual homework assignments, but also self-study problems, puzzles, etc.
Can I ask a homework question here?
Yes, but there are a couple of things you need to make sure of first.
As a general rule, we do not discourage homework questions, as long as they are related to physics. But do keep in mind that Physics Stack Exchange is not primarily a homework help site; it's a place to get specific conceptual physics questions answered. Thus, not all homework questions are on topic, and you should check the meta thread to see how to ask an on-topic one.
Additionally, if your question is part of a homework assignment or other such work under a honor code, you should check with your institution, and teacher whether it's OK to ask for help online and to post the problem on a public site.