The position of a particle as a function of time ‘\( t \)’, is given by \( x(t)=at+bt^2-ct^3 \), where \( a \), \( b \) and \( c \) are constants. Then velocity of particle when acceleration becomes zero is:
\( a+\dfrac{b^2}{3c} \)
\( b+\dfrac{a^2}{3c} \)
\( a-\dfrac{b^2}{3c} \)
\( b-\dfrac{a^2}{3c} \)