In Figure $(\backslash ($ a $\backslash )),$ a block of mass $\backslash ($ m $\backslash )$ lies on a horizontal frictionless surface and is attached to one end of a horizontal spring $($spring constant $\backslash ($ k $\backslash ))$ whose other end is fixed. The block is initially at rest at the position where the spring is unstretched $\backslash (($x$=0)\backslash )$ when a constant horizontal force $\backslash (\backslash$overrightarrow$\{\backslash$mathbf$\{$F$\}\}\backslash )$ in the positive direction of the $\backslash ($ x $\backslash )$ axis is applied to it$.$ A plot of the resulting kinetic energy of the block versus its position $\backslash ($ x $\backslash )$ is shown in Figure $(\backslash ($ b $\backslash )).$ The scale of the figure's vertical axis is set by $\backslash ($ K$\_\{$s$\}=2\mathrm{.}8\backslash$mathrm$\{$~J$\}\backslash )$ and the scale of the figure's horizontal axis is set by $\backslash ($ x$\_\{\backslash$text $\{$max $\}\}=4\mathrm{.}0\backslash$mathrm$\{$~m$\}\backslash ).$

$($a$)$ What is the magnitude of $\backslash (\backslash$mathbf$\{$F$\}\backslash )?$

N

$($b$)$ What is the value of $\backslash ($ k $\backslash )?$

N$/$m