@dalehileman,
However, why didn't you consider doing a Google research, to which you are usually so prone, about this topic?
You would see that there are:
871 hits for "capable in physics".
109 hits for "capable at physics"
For the latter, it's mostly people posting on forums (fora).
For the former, mainly books, like here:
Quote:Evidently Einstein considered himself equally capable in physics and philosophy but decided that a primary concentration on physics would be more rewarding.