I crashed H Physics in sixth year. I had a really good teacher and managed to get an A, even though I didn't do nat 5. There isn't a lot of nat 5 physics in it, and if there is- it's nothing too complex. Since you're doing AH Chemistry, there's a wee bit of overlap with some of the concepts believe it or not such as atomic emission (Bohr theory/Planck), etc. I didn't enjoy Physics too much but I still found it rather easy to deal with.
I'd say there's no harm in trying it. From experience, there's no point keeping going with the N5 when you'll be accustomed to a higher level of demand. To answer your question, if you're willing to try and understand the course and work hard, an A is not impossible at all. Plus, it's really easy to do well in the assignment if you listen to your teacher and follow all the guidance documents.