Two identical first-order systems have been cascaded non-interactively.

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Two identical first-order systems have been cascaded non-interactively. The unit step response of the systems will be—

1. overdamped
2. underdamped
3. undamped
4. critically damped

Correct Option: D

According to the equation, two identical first order systems have been cascaded non-interactively
i.e.,
(1 + sT) (1 + sT)
C.E. (1 + sT) (1 + sT) = 0
⇒ s²T² + 2sT + 1 = 0

⇒ s² +	2s	+	1	= 0
	T		T²

2ξ ωn = 2/T
ω_n² = 1/T²
or
ω_n = 1/T

ξ =	1	=	1	= 1
	Tω_n		T(1/T)

Hence alternative (D) is the correct choice.