Chapter 12 - Section 12.5 - Tangential and Normal Components of Acceleration - Exercises - Page 668: 2

$a=0 \ T + 0 \ N$

$v(t)=\dfrac{dr}{dt}=3i+j-3k$ or, $|v(t)|=\sqrt {(3)^2+(1)^2+(-3)^2}=\sqrt {19}$ Now $a(t)=\dfrac{dv(t)}{dt}= 0 $ or, $|a(t)|=\sqrt {0} \implies |a(t)|=0$ $a_{N}=\sqrt {|a|^2 -a^2_{T}}=\sqrt {(0)^2-(0)^2}=0$ and $a=a_T T+a_{N} N=0 \ T + 0 \ N$