Displacement-time equation of a particle moving along x-axis is $x=20+t^3-12t\text{ (SI units) }$. Find position of particle when velocity of particle is zero. 

Substituting v =0 in $v=\frac{dx}{dt}=3t^2-12$, we have $0=3t^2-12$.

Positive value of t comes out to be 2 s from this equation. Substituting t = 2s in $x=20+t^3-12t$. 

$x=20+(2{)}^3-12(2)\text{ or }x=4 \mathrm{m}$