Consider the closed loop system shown in the figure below R

$($a$)$ Assuming that $g_m(s)=1,$ obtain the closed loop characteristics polynomial of the system and hence or otherwise determine the range of values of $K_c$ for the system to closed loop stable.

$($b$)$ With $K_c=2,$ obtained the closed loop transfer function $J(S)=y\frac{S}{r}(S).$ Obtain the unit step response of $y(t).$ Show details solutions without you explaining it in sentences form. Just show the calculation solving for the answers