The $2-$kg block is subjected to a force having a constant direction and a magnitude $F=(\frac{600}{2+s})N,$ where $s$ is in meters. When $s=6m,$ the block is moving to the left with a speed of $7\mathrm{.}9\frac{m}{s}.$

$($Figure $1)$

Figure

$1$ of $1$

Part A

Determine its speed when $s=18m.$ The coefficient of kinetic friction between the block and the ground is ${}_k=0\mathrm{.}25.$

Express your answer to three significant figures and include the appropriate units.