Let's say there are two objects going nearly the speed of light, in opposite directions.

[![Object 1 and 2 moving in opposite directions](https://i.stack.imgur.com/gC8Jc.png)](https://i.stack.imgur.com/gC8Jc.png)

Obviously from the vantage point of #1, #2 would be moving at about the speed of light, c. But assuming #1 thought it was stationary, what would be the perceived energy of #2 from the perspective of #1? In my mind it seems like this would make sense since the remaining energy wouldn't go into making it move faster

$E^{2} = (mc^2)^2 + (pc)^2$

$E^{2} = (mc^2)^2 + (mc\*c)^2$

$E = \sqrt{2}mc^2$

But I could also see the answer just being this:

$E = 2mc^2$

And I could also see myself being completely wrong on both fronts.

Thanks for your time. I apologize if this has already been asked before, but all I could find were questions like [this](https://physics.stackexchange.com/q/11398/), which, while the question sounds similar it is fundamentally a different question.