The distance travelled by a particle is related to time \( t \) as \( x = 4 t^2 \). The velocity of the particle at \( t = 5 \, \text{s} \) is:
\( 8 \, \text{ms}^{-1} \)
\( 25 \, \text{ms}^{-1} \)
\( 20 \, \text{ms}^{-1} \)
\( 40 \, \text{ms}^{-1} \)