Vector Differentiation with Unit Vectors and Constant Components

[karnten07]

Homework Statement

Differentiate:

v = 2at x + 3bt^2 y + cz

w.r.t time to get a

where x, y and z are unit vecotrs and should have hats above them

Homework Equations

The Attempt at a Solution

I get a = 2a x + 6bt y + z

But I am not sure if that z should completely disappear or not?

 

[dynamicsolo]

If c is a constant, then the derivative will be zero for the z component. (After all, the original specification for v says that the vector field everywhere has a constant z-component and hence a constant inclination to the xy-plane.)