Explanation

For a standard form $\frac{\omega_n^2}{s^2 + 2\zeta\omega_n s + \omega_n^2}$, we have $2\zeta\omega_n = 2$, so $\zeta\omega_n = 1$. Also, $\omega_n^2 = 4$, meaning $\omega_n = 2$. Thus, $\zeta(2) = 1$, and the damping ratio $\zeta = 0.5$.