Correct Answer - Option 2 : 8.8 rad/sec

__Concept:__

Damped natural frequency of a second order system is given by

\({ω _d} = {ω _n}\sqrt {1 - {\xi ^2}} \)

Where,

ωn = Natural frequency

ζ = Damping ratio

__Calculation:__

Given-

ωn = 11 rad/sec

ζ = 0.6

Now, natural damped frequency can be calculated as

\({ω _d} = {11}\sqrt {1 - {(0.6)^2}} \)

ωd = 11 x 0.8

ωd = 8.8 rad/sec