It has been a while since I have taken derivatives, but I know the basic rules... I am just having trouble understanding what is constant and what is a variable. Could you help me out with the second derivative of this function?
I assume that you meant to include the red dashes to denote derivative ...? Your derivatives are correct. Now you have to differentiate again to get the second derivative of the vector function.
By the way, note that the derivatives by themselves are not the answer to the question.