The question Why is friction force negative in ice skater problem?Why is friction force negative in ice skater problem? is awesome. It gives the problem, what the OP did to solve it, and then it asks a conceptual question about something that didn't make sense to the OP. They got the answer correctly and the question shows a clear desire to learn more about the actual physics. This is the ideal we all look for.
replaced http://physics.stackexchange.com/ with https://physics.stackexchange.com/