The URL will be structured by using the question title not the content of the question or answer .
So try to edit the question title according to you need the URL to be midified . This helps in SEO page ranking .
There is a method qa_q_request() in qa-base.php , which returns the Q2A request for question $questionid, and make it search-engine friendly based on $title, which is shortened if necessary by removing shorter words which are generally less meaningful.
If you want to modify its behaviour then you might create a plugin that overrides the behavious this function .