Hi, I am a freshman in high school (going into sophomore next September) and am trying to prepare for the IPhO. I was recommended to use Resnick and Halliday to learn the physics, and am currently doing that. However, I am still unable to solve USAPhO problems in areas that I have covered in Resnick and Halliday. How should I bridge the gap between Resnick and Halliday problems to USAPhO problems so that I am able to solve the harder USAPhO and IPhO problems? Also, how much calculus do I have to know for the USAPhO and IPhO? I am taking Calc BC next year, but I do not know if that is enough. Is there other math that I must learn?