Control Systems: Part2 Objective Questions

[1] The system represented by the input-output relationship y(t)= ^5t∫_-∞ x(τ)dτ, t>0 is

(a) Linear and casual

(b) Linear but not casual

(c) Casual but not linear

(d) Neither linear nor casual

Ans: B

[2] For the system 2/(s+1), the approximate time taken for a step response to reach 98% of its final value is

(a) 1s

(b) 2s

(c) 4s

(d) 8s

Ans: C

[3] Given the finite length input x[n] and the corresponding finite length output y[n] of an LTI system as shown below, the impulse response h[n] of the system is         

(a) h[n]={1,0,0,1}

(b) h[n]={1,0,1}

(c) h[n]={1,1,1,1}

(d) h[n]={1,1,1}

Ans:C

[4] The frequency response of G(s)=1/[s(s+1)(s+2)] plotted in the complex G(jω) plane (for 0< ω<∞) is....Options A, B, C, D are given below

  A.                                                                                                          

                                         

   

Ans:A

[5] The system x=Ax+Bu with

 A=

                                    

B=  

   

is


(a) Stable and controllable

(b) Stable but uncontrollable

(c) Unstable but controllable

(d) Unstable and uncontrollable

Ans: C

[6] The characteristic equation of a closed-loop system is a(s+1)(s+3)+k(s+2)=0,k>0. Which of the following statements is true?

(a) Its roots are always real

(b) It cannot have a breakaway point in the range -1<Re[s]<0

(c) Two of its roots tend to infinity along the asymptotes Re[s]=-1

(d) It may have complex roots in the right half plane

Ans:C

[7] The frequency response of a linear system G(jω) is provided in the tabular form below 

|G(jω)|	1.3	1.2	1.0	0.8	0.5	0.3
∠G(jω)	-130°	-140°	-150°	-160°	-180°	-200°

(a)  6dB and 30°

(b)  6dB and -30°

(c)  -6dB and 30°

(d)  -6dB and -30°

Ans:A

[8] An openloop system represented by the transfer function G(s) = [(s+1)/(s+2)(s+3)] is

a) Stable and of the minimum phase type

b) Stable and of the non-minimum phase type

c) Unstable and of the minimum phase type

d) Stable and of the non-minimum phase type

Ans:D

[9] The open loop transfer function G(s) of a unity feedback control system is given as, G(s)=[ k(s+2/3) / s²(s+2) ] From the root locus, it can be inferred that when k tends to positive infinity.

(a)  Three roots with nearly equal real parts exist on the left half of the s-plane

(b)  One real root is found on the right half of the s-plane

(c)  The root loci cross the jω axis for a finite value of k; k not equal to 0

(d)  Three real roots are found on the right half of the s-plane

Ans:A

[10] The response h(t) of a linear time invariant system to an impulse δ(t), under initially relaxed condition is h(t) = e^-t+e^-2t. The response of this system for a unit step input u(t) is

(a)   u(t)+e^-t+e^-2t

(b)   (e^-t+e^-2t) u(t)

(c)   (1.5-e^-t-0.5e^-2t) u(t)

(d)   e^-tδ(t)+e^-2tu(t)

Ans:C