Kinetic energy is 0.5 mv^2. Then let's say v = c, the speed of light. This means that if a one kilogram object moves at the speed of light, it has 44,937,759 Gigajoules of energy.

What if you theoretically had that much energy and you used it all to accelerate an object which weighs one kilogram. Wouldn't it then move at the speed of light of faster?