$$\text { Find the tangential component of the acceleration vector. }$$

Short Answer

$$\text { A particle moves with position function } \mathbf { r } ( t ) = \left( 21 t - 7 t ^ { 3 } - 5 \right) \mathbf { i } + 21 t ^ { 2 } \mathbf { j } \text {. }$$ $$\text { Find the tangential component of the acceleration vector. }$$