As a rough rule, relativistic effects only become important for back-of-the-envelope calculations past about 0.5c; they become dominant past about 0.9c. Newtonian calculations are good enough for rough calculations at lower velocities. The two are nearly indistinguishable below about 0.05c.

On Wed, Jan 14, 2015 at 10:47 AM, David Shaw <dj.shaw@btconnect.com> wrote:

I have never attempted relativistic calculations before and wondered if
I have this right.

I am currently reading John Ringo's 'Gust Front' in which a ground based
anti-starship weapon is described as firing bars of depleted uranium,
100mm in diameter and two metres long at a muzzle velocity of 0.3c.

I make this a KE of 1.302 exa-Joules, equivalent to a touch over 311MT
of TNT. Is this right? And would such a weapon system really be
feasible within an Earth-standard atmosphere?

Many thanks,

David Shaw
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