I am going into year 9 this year (Sep 2019), and am passionate about physics; is it too late for me to thoroughly prepare for the competition if I wish to participate in year 11, taking into account that I have not seriously started learning trigonometry yet? I plan to do some self-study first, and I wonder where I might get started. Also, apart from the olympiad, what are some other competitions related to physics which I might be able to take part in? Thanks for any advice on this.
Sorry this is kind of late. But, if you are currently in 9th grade, I HIGHLY recommend that you spend time over the summer to prepare for the F=ma Exam, which is the Open Exam (tests in only Mechanics) and qualifies you to participate in the US Physics Olympiad. The US Physics Olympiad tests you in topics across all fields of physics, but it shouldn’t be too hard to do well as long as you study the right materials.
Now to more direct this message towards you, I also highly recommend that you learn vectors and trigonometry before starting; these are the fundamental mathematical concepts you need to know before doing physics. I would also recommend you to start learning a bit of calculus, which would help you gain much intuition in problem solving.
As for other competitions, there is PUPC at Princeton and also OPhO (Online Physics Olympiad). Be sure to check it out at http://physoly.tech/opho/ !!