My empire's flagship, the Persecutor class UJBHE1 Abhorrent, rides into the home system of my greatest enemy, Baron Obsequious, levels its Death Ray2 at his beloved home, and pulls the trigger.3 Baron Obsequious' prized emerald explodes in a shower of light that would make George Lucas proud.
Given that the Abhorrent's defense screens can only absorb 100 TJ of electromagnetic or kinetic energy before critically compromising the ship (i.e., the ship must withstand less than 100 TJ throughout the experience or the deal's off)...
Assume the cross-section of the ship is one square kilometer (thanks Mark!)
Assume the Abhorrent is using thrust to hold a static position away from the planet. It's not in orbit. (Thanks again, Mark!)
How far away must the Abhorrent be to survive the blast?
At that distance, will the "sudden"4 dispersal in mass result in a change of gravity that will cause the ship to lurch backward (away from what was once Baron Obsequious)?
1 Representing the Universal JBH Empire dontchaknow.
2 Because no name for an energy weapon can possibly be better than anything used during the Flash Gordon era.
3 Only wusses use buttons.
4 And here I need to make a choice. "Sudden" on a plantary scale may render the question moot. Let's assume, as impossible as it may be, that the mass disperses to basically 0% of its original density within 5 minutes of triggering the ray. That's 0.333%/second or a loss of 0.184g/cm3 per second.