reality is a pretty good simulation of SpaceEngine?

I look forward to the day that Space Engine simulates a universe containing itself.

Gee Harliquin, what are you trying to calculate?  (What is your input?)

As Hornblower said, it should have no trouble doing acceleration.  WolframAlpha is really good at figuring out the units (or 'dimensions') of the quantity you're interested in and converting them accordingly, even if the quantities you put in are in all sorts of different units.  (I think this is actually one of its best features).  So if it's not giving you acceleration out, then probably whatever you're putting in is not actually equivalent to acceleration.

For example, you can put in (10 Newtons)/(25 milligrams), and it correctly converts the answer to acceleration, in meters per second squared.  Or you can put in 2*G*(10 solar masses)/c^2, and it converts the answer to distance, which in this case is the size of the event horizon of a 10-solar-mass black hole.

Ah, you are asking for velocity, which is distance per time.  Distance/sec^2 is acceleration, which is different.  You can't convert velocity to acceleration anymore than you can convert meters to kilograms.  So... just divide the distance by the time in Wolfram Alpha, and it will tell you the velocity you need.

If you did want the answer in distance/sec^2, then the question you would be asking is "what acceleration do you need (presumably a constant acceleration) to make the journey in that time."  If that is what you want, then okay, it's just more math and you'll need to use a formula.