Stats for a high speed space cannon

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So out of boredom I decided to make a "prototype" of a giant space cannon. Basically, it fires a projectile at a significant fraction of the speed of light to get a huge amount of kinetic energy. I basically just spent the past two hours putting in different numbers into the equation and coming up with what I liked. Funny note, I started of with the Newtonian equation for kinetic energy (K=.5mv^2) not realizing it totally falls apart at high speeds. Anyways, I'm not too concerned about accuracy as long as it is somewhat close, but here is what I have.

A cylindrical lithium shell 2.75m length x 1m radius with a total mass of 463kg is fired at 10% of the speed of light for a total kinetic energy of 2.092x10^17 joules, or 50,000 kilotons of TNT. This is the same amount of energy as the Tsar Bomb.

Please point out if I missed anything obvious, I wouldn't be very surprised if I did. Also, when this thing hits, say, a space ship, how would that play out? Would it cause a massive explosion, or would it pass straight through, or some combination?

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The energy looks about right. Around 10% of light speed the Newtonian equation is still reasonably accurate.

As for what would happen, well xkcd discusses hypervelocity impacts, https://what-if.xkcd.com/20/ He doesn't specifically address 0.1c though, jumping from 0.01c to 0.99c.

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You are not describing how you plan to reach that speed. Just detonating and somehow magically containing a Tsar bomba won't do.

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