Create a field function
 

Hello everybody
I did a stationary simulation and a rigid body motion simulation of the overtaking process so now I have to compare the results obtained. For this reason I tried to create, for stationary simulation, a new vector field function, relative velocity, that is, the vector velocity at which I subtract 10 m/s(the velocity of the moving car) along the X-direction(the direction of the motion).
could anyone help me?
many thanks

And what is your problem with this?

the problem is that I'm not able to create this vector field function.
could you tell me how to do it???
thanks