Equation of displacement for any particle is $s = 3{t^3} + 7{t^2} + 14t + 8m$. Its acceleration at time $t = 1\, sec $ is.......$ms^{-2}$

A particle is moving in one dimension (along $\mathrm{x}$ axis) under the action of a variable force. It's initial position was $16 \mathrm{~m}$ right of origin. The variation of its position ( $\mathrm{x}$ ) with time ( $\mathrm{t})$ is given as $\mathrm{x}=-3 \mathrm{t}^5+18 \mathrm{t}^2+16 \mathrm{t}$, where $\mathrm{x}$ is in $\mathrm{m}$ and $\mathrm{t}$ is in $\mathrm{s}$. The velocity of the particle when its acceleration becomes zero is________ $\mathrm{m} / \mathrm{s}.$

Give examples of a one - dimensional motion where
$(a)$ The particle moving along positive $x- $ direction comes to rest periodically and moves forward.
$(b) $ The particle moving along positive $x-$ direction comes to rest periodically and moves backward.

If the displacement of a particle varies with time as $\sqrt{x}=t+7$, then