I can't speak for physics, but I agree computational biology is very broad. Like say the methods used in computational neuroscience I imagine is heavy on differential equations to simulate the dynamics of neurons firing and such, while computational genomics aka bioinformatics, the area I work in, uses completely different methods (variants of string matching/edit distance algorithms, statistics, machine learning) where numerical methods may not even be the best place to start. OP, you need to narrow down the scope of your question. If you haven't already, learn the basics of physics and biology from a survey course or even a popular science book and pick a couple areas to narrow it down.