Hey there!
According to you, what do you think is the hardest topic in physics 3/4? And are the checkpoint questions helpful? Are there are any other resources you used for physics practice questions? Thank you!!
I can't comment on what resources are helpfull as I haven't really had time to use them (I am only studying physics 3/4 this year), but I can say that I am using checkpoints and intend to get the ATAR notes books soon aswell.
As for the hardest topic, I have been told by my physics teacher and some students who did 3/4
this last year (still getting used to it being 2019) that waves and light were the hardest topics, especially since they are quite new ideas that aren't really covered in previous years. That being said, I do believe that the 'hardness' of topics will change from person to person as different people take interest in different areas of physics, and having an interest certainly makes things a whole lot easier to learn.
Hopefully, this helps and good luck to you this year in physics! (I assume you are studying it this year)