the theory when I was in school was you had to have a year of calculus before you took physics. Calculus made no sense to me until I took physics, then I began to see the beauty, symmetry, and logic of the natural world. I think calculus an physics need to be taught concurrently. The connection between mathematics and the physical world needs to be demonstrated from day one.
Absolutely! To teach newtonian physics and/or calculus separately makes both of them harder. Mechanics is the easiest way to make the concepts of calculus real...