The Normal Component $a _ { \mathrm { N } } ( t )$

Multiple Choice

The normal component $a _ { \mathrm { N } } ( t )$ of the acceleration of a particle moving along the curve $\mathbf { r } ( t ) = e ^ { t } \mathbf { i } + e ^ { - t } \mathbf { j } + t \mathbf { k }$ is

A) $\frac { 3 } { \sqrt { 2 } }$
B) $\frac { \sqrt { 2 } } { 3 }$
C) $\sqrt { 56 }$
D) 1
E) 0