Answer 2 isn't strictly true. Mass increases with any velocity increase, although it's negligable (but not zero) until you approach speed of light.
Because mass increases you need an increasing amount of enery to get the same increase in velocity. As you get very close to the speed of light, mass increases exponentially (zooms off to infinity) such that you would need an infinite amount of enery to accelerate any more. That is why nothing can travel faster than light.
Answered Wed 10th October, 2012 @ 15:37 by Robotperson Edited by Robotperson on Wed 10th October, 2012 @ 15:43