Incorrect notion: "From my knowledge mass of an object decreases if the object is accelerated making energy constant"... You are slightly confused here. It is the opposite. The mass increases as a particle speeds up. As the velocity approaches "c", the mass is so large that any added energy is not sufficient to raise the velocity beyond "c". Thats the way mother nature does it. For example, a rocket accelerates only after gaining more Kinetic energy from some other source of energy-maybe chemical energy in fuel. Although, the total energy of the system (rocket's KE + fuel's Chemical energy) remains constant, the Kinetic energy of the rocket surely builds up at the expense of fuel's chemical energy. Another note to anyone interested: IN my experience, our undergrad physics stops around 1940's. Mostly, our teachers are unable to explain us the modern physics and/or we soon lose interest. In the last 60 years or so, QED and other quantum theories have taken over physics. Every earlier theory, except gravitation and nuclear reaction, has been beautifully explained by the quantum theory. Physicists' quest now is to find a unified theory- that can unite the quantum theory (theory of the smallest scale) and gravitation (theory of the large).