Well, until now. In calculus, you're just deriving and integrating functions, evaluating expressions, simplifying functions, and executing them, etc. I don't think it takes that much brain power to do the same mundane operations when everything (minus the variable you wish to solve for) is clearly spelled out for you. In physics, you have to do a bit more thinking, I believe. Like, you're supposed to figure out on your own what all the variables are, and ask yourself questions on the values of those variables. "Is velocity decreasing or increasing?", "Is this value positive or negative?" It may just be me, though.