Control Systems
Time response for a second order system depends on the value of τ. If τ= 0 then the system is called as

  undamped system.
  over damped system.
  critically damped system.
  under damped system.

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Control Systems
A cascade of three linear time invariant systems is causal and unstable. From this we conclude that

 at least one system is unstable and at least one system is causal.
 at least one system is causal and all systems are unstable.
 the majority are unstable and the majority are causal.
 each system in the cascade is individually caused and unstable.

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