Physics AS is a piece of cake, no excuse not to get a B. Physics A2 on the other hand is a completely different ball game.
The maths side is simple enough - you just have to have that mathematical mind-set, thinking logically through questions. imo, the issue with Physics A2 is that you can't be a lazy student; it will take up all of your time, I guarantee it. I ended up with a C overall, got an A in AS and I-don't-even-know in A2. In the ISA I got a C and in unit 5 I got a high D (not very good at radioactivity) and in unit 4 I got a D also. Just not in the multiple choice. I scored 5/25 in the multiple choice. It's horrific.
So with the multiple choice you face a fork in the road, either focus shitloads of your revision time (~60%) memorising and practising or don't and fail. With the U from the multiple choice, I got a (high) U overall in unit 4. Unless your preferred degree needs Physics, do a different subject (ie: Chemistry, Maths etc.)