you can take 1/(s-1)(s2 + k2) and break it up into A/(s-1) + (Bs + C)/(s2 + k2) to get
A = 1/(1 + k2), B = -1/(1 + k2), and C = -1/(1 + k2) Let 1/(1 + k2) = p = constant
then you have Y(s) = p/(s-1) - ps/(s2 + k2) - p/(s2 + k2)
to find that y(t) = pet - pcos(kt) - (p/k)sin(kt)