Question: Why can I answer only a limited amount of questions a day? 

Answer: It's a spam control measure.  Basically it's to keep people from submitting hundreds of questions a day as a form of advertising, etc.  Once you level up (mainly by having people accept answers that you've written, or by accepting other people's answers) you can answer more, because you've generated some trust with the system.  Once you get to Level 5, you can answer an unlimited number of questions.
This question from the Yahoo Q&A forum is categorized in the topic: Computers & Internet