It's fair to say that your original question has raised some vigourous debate as per Vincent's comment. I personally didn't engage in that debate directly but I did follow it closely, and you'll note that I did attempt to make an initial edit to get this question going in the right direction.
Ultimately, the problem that most people have with this question in this forum boils down to 'fitness'. In its original form, it was poorly worded and looked like a simple physics question, to which most people will say 'well what difference does it make to your fictional world?' leaving you with a question that can be answered simply by plugging in the Earth's mass into E=mc^2 which would be considered too lightweight by the Physics SE crowd, but off topic here.
Despite this, the question about a large planet colliding with the sun was NOT closed as being off topic. On the surface, they would appear to be similar insofar as both could essentially be answered by some form of physics, but this question brought with it some sense of speculation that (respectfully), yours didn't.
Another way of putting this; your question originally asked for a value, not an effect. The other question actually asks whether the sun would dim or brighten, how long the effect would last for, what it would look like from the standpoint of the Earth.
If you were to follow the same principle, then your question needs to be edited to ask about effects; how far away would the collision be visible? how quickly would the planets collide, and would the energy being generated at their contact plane be sufficient to either slow (or even reverse) the effect of gravity? Would it appear like a supernova, and does the energy created by a matter / antimatter reaction generate cosmic rays or pure radiant heat? Can other planets in the system where this happens survive, and what impacts would it have on the habitability of those planets over the long term? Would it (for instance) vaporise or sterilise all planets within the solar system in which the collision takes place?
Why did I first try to edit your question in the first place? Because it's actually a GOOD question if you look at the spirit of what you're asking. Every bit as good as the question about planets colliding with a Sun. BUT, if all you ask for is a number, you haven't intrigued anyone. You haven't asked them to extrapolate outcomes from the numbers they can derive. You haven't asked them to speculate.
That is ultimately what the people on this site love doing. Inspire us to imagine new effects in the context of our engineering / analytics / economics / biological / physics / chemistry / etc. backgrounds, and we'll jump at the challenge.
Could this have been pointed out a little better at the outset? Probably. But, for people capable of providing answers to impossible or crazy situations, we seem singularly unable to articulate what sort of questions we like. This is in part because we rule by committee, but I also think it's because the scope of this site is somewhat ambiguous to begin with.
It is important to note that you should take most of what I say with a grain of salt; my first (and only) attempt to ask a question on worldbuilding failed catastrophically and ever since then I've constrained myself to answers, which (for the most part) seem to be far better received. That said, my personal view on how to fix your question would be to focus on the effects, not the math.
Put a hard-science tag on the question by all means, but the answer shouldn't be a number of joules; it should be an impact. That would at least satisfy the world-building element, and allow people to come up with their own ideas about how such a collision would occur, and how your world would experience it from afar (however far away that is as defined by your brief).
Of course, as a final warning, don't just cut and paste all the sample questions from my 5th paragraph into a single question post. We still work on 1 question per post, but (hopefully) these questions give you a method for expanding your question into a series of related questions that can all provide some value across different contexts of your story.
In short; persist with it. I'd really like to see some answers to some of the questions postulated above and it's an interesting concept to be sure. Yes, there is still some subjectivity to this question and I cannot guarantee that if you follow my advice you'll be better received, but I for one would like to see what happens if you try.
