How to make MuPad know a variable is independent to another

I am working on Lagrange's equation of mechanics. How can I make MuPad know that x(t) and y(t) (position in different dimensions) are independent to one another so that diff(x(t),y(t))equal zero. Another question is that how to write MuPad code for partial derivative between x'(t)(velocity) and x(t) to be zero.

Answer 1

[Walter Roberson]

You can only differentiate something with respect to a free variable, so diff(x(t),y(t)) is not a valid computation.

I do not know what your notation x'(t)(velocity) is intended to indicate, exactly ?