5 The position vector \(\mathbf { r }\) metres of a particle at time \(t\) seconds is given by
$$\mathbf { r } = \left( 1 + 12 t - 2 t ^ { 2 } \right) \mathbf { i } + \left( t ^ { 2 } - 6 t \right) \mathbf { j }$$
- Find an expression for the velocity of the particle at time \(t\).
- Determine whether the particle is ever stationary.