Mathematics Advanced or Mathematics Extension 1 would be quite adequate for HSC Physics. In my experience, you have to distinguish between students who have two types of mathematical ability. There are students who are good at crunching formulae and numbers (which I call formulaic maths) and students who think mathematically and can apply mathematical ideas to solve problems (the problem solvers). To excel at HSC Physics, you need more problem solving ability, and less formulaic maths. After all, the formulae are all given to you in the data sheet. Knowing which formula you should use is the hard part. I have known quite good students who pride themselves on formulaic maths who got frustrated with Physics (and to some extent Chemistry as well) because they could not understand the questions, and frequently made conceptual mistakes. So, my advice - focus on problem solving.