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Signals and Systems
Laplace Transform

Practice questions from Laplace Transform.

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Q#1 Laplace Transform GATE EC 2016 (Set 1) MCQ +2 marks -0.66 marks

The Laplace transform of the causal periodic square wave of period T shown in the figure below is

Q

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Q#2 Laplace Transform GATE EC 2016 (Set 1) MCQ +2 marks -0.66 marks

A first-order low-pass filter of time constant T is excited with different input signals (with zero initial conditions up to t = 0). Match the excitation signals X, Y, Z with the corresponding time responses for t ≥ 0:

X: Impulse                 

Y: Unit step         

Z: Ramp         

X–>R, Y–>Q, Z—>P        

X–>Q, Y–>P, Z—>R

X–>R, Y–>P, Z—>Q        

X–>P, Y–>R, Z—>Q

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Q#3 Laplace Transform GATE EC 2016 (Set 2) NAT +1 mark -0 marks

The response of the system  to the unit input u(t) is y(t). The value of at is _____________.

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Q#4 Laplace Transform GATE EC 2015 (Set 2) MCQ +1 mark -0.33 marks

Let the signal  outside the interval  where  and  are finite. Furthermore, . The region of convergence (ROC) of the signal’s bilateral Laplace transform F(s) is

A parallel strip containing the jΩ axis

A parallel strip not containing the jΩ axis

The entire s-plane

A half plane containing the jΩ axis

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Q#5 Laplace Transform GATE EC 2015 (Set 2) MCQ +1 mark -0.33 marks

By performing cascading and/or summing/differencing operations using transfer function blocks  and, one CANNOT realize a transfer function of the form

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Q#6 Laplace Transform GATE EC 2015 (Set 2) MCQ +2 marks -0.66 marks

Input x(t) and output y(t) of an LTI system are related by the differential equation . If the system is neither causal nor stable, the impulse response h(t) of the system is

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Q#7 Laplace Transform GATE EC 2015 (Set 2) NAT +2 marks -0 marks

Let  with , where u(t) is unit step function. If the bilateral Laplace transform of x(t) is  

Then the value of β is __________.

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Q#8 Laplace Transform GATE EC 2014 (Set 1) MCQ +2 marks -0.66 marks

A system is described by the following differential equation, where u(t) is the input to the system and y(t) is the output of the system. . When y(0)=1 and u(t) is a unit step function, y(t) is

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Q#9 Laplace Transform GATE EC 2014 (Set 3) NAT +1 mark -0 marks

The input , where u(t) is the unit step function, is applied to a system with transfer function  .If the initial value of output is -2, then the value of the steady state is ___________.

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Q#10 Laplace Transform GATE EC 2014 (Set 3) MCQ +2 marks -0.66 marks

Let h(t) denote the impulse response of a causal system with transfer function .

Consider the following three statements.

S1: The system is stable.

S2:   is independent of t for t>0.

S3: A non-causal system with the same transfer function is stable.

For the above system,

only S1 and S2 are true         

only S2 and S3 are true

only S1 and S3 are true         

S1, S2 and S3 are true

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Q#11 Laplace Transform GATE EC 2014 (Set 4) MCQ +2 marks -0.66 marks

A stable linear time invariant (LTI) system has a transfer function  . To make this system causal it needs to be cascaded with another LTI system having a transfer function . A correct choice for  among the following options is

s+3

s-2

s-6

s+1

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Q#12 Laplace Transform GATE EC 2014 (Set 4) NAT +2 marks -0 marks

A causal LTI system has zero initial conditions and impulse response h(t). Its input x(t) and output y(t) are related through the linear constant-coefficient differential equation

 .         

Let another signal g(t) be defined as

 .

If G(s) is the Laplace transform of g(t), then the number of poles of G(s) is _______.

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Q#13 Laplace Transform GATE EC 2013 (Set 1) MCQ +1 mark -0.33 marks

Assuming zero initial condition, the response y(t) of the system given below to a unit step input u(t) is

5.jpg

u(t)

t u(t)

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Q#14 Laplace Transform GATE EC 2013 (Set 1) MCQ +2 marks -0.66 marks

A system is described by the differential equation. Let x(t) be a rectangular pulse given by . Assuming that  and  at , the Laplace transform of y(t) is

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Q#15 Laplace Transform GATE EC 2013 (Set 1) MCQ +2 marks -0.66 marks

A system described by a linear, constant coefficient, ordinary, first order differential equation has an exact solution given by y(t) for , when the forcing function is x(t) and the initial condition is y(0). If one wishes to modify the system so that the solution becomes  for  , we need to

Change the initial condition to  and the forcing function to

Change the initial condition to  and the forcing function to

Change the initial condition to  and the forcing function to

Change the initial condition to  and the forcing function to

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Q#16 Laplace Transform GATE EC 2012 (Set 1) MCQ +1 mark -0.33 marks

A system with transfer function  is excited by sin (ωt).

The steady-state output of the system is zero at

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Q#17 Laplace Transform GATE EC 2011 (Set 1) MCQ +1 mark -0.33 marks

The differential equation  describes a system with an input x(t) and an output y(t). The system, which is initially relaxed, is excited by a unit step input.

The output y(t) can be represented by the waveform

1.jpg

2.jpg

3.jpg

4.jpg

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Q#18 Laplace Transform GATE EC 2011 (Set 1) MCQ +1 mark -0.33 marks

If the unit step response of a network is .

Then its unit impulse response is

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Q#19 Laplace Transform GATE EC 2011 (Set 1) MCQ +2 marks -0.66 marks

An input  is applied to an LTI system with impulse response.

The output is

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Q#20 Laplace Transform GATE EC 2011 (Set 1) MCQ +2 marks -0.66 marks

If  then the initial and final values of f (t) are respectively

0, 2

2, 0

0, 2/7

2/7, 0

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Q#21 Laplace Transform GATE EC 2010 (Set 1) MCQ +1 mark -0.33 marks

A system with the transfer function  has an output  for the input signal . Then, the system parameter ‘p’ is

1

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Q#22 Laplace Transform GATE EC 2010 (Set 1) MCQ +1 mark -0.33 marks

A continuous time LTI system is described by .

Assuming Zero initial conditions, the response y(t) of the above system for the input  is given by

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Q#23 Laplace Transform GATE EC 2008 (Set 1) MCQ +1 mark -0.33 marks

The impulse response h(t) of a linear time-invariant continuous time system is described by , where u(t) denotes the unit step function, and  and  are real constants. This system is stable if

 is positive and  is positive

 is negative and  is negative

 is positive and  is negative

 is negative and  is positive

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Q#24 Laplace Transform GATE EC 2008 (Set 1) MCQ +2 marks -0.66 marks

A linear, time-invariant, causal continuous time system has a rational transfer function with simple poles at s = -2 and s = -4, and one simple zero at s = -1. A unit step u(t) is applied at the input of the system. At steady state, the output has constant value of 1. The impulse response of this system is

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Q#25 Laplace Transform GATE EC 2007 (Set 1) MCQ +1 mark -0.33 marks

If the Laplace transform of a signal y(t) is  then its final value is

-1

0

1

Unbounded

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Q#26 Laplace Transform GATE EC 2007 (Set 1) MCQ +2 marks -0.66 marks

The frequency response of a linear, time-invariant-system is given by. The step response of the system is

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Q#27 Laplace Transform GATE EC 2006 (Set 1) MCQ +2 marks -0.66 marks

The unit-step response of a system starting from rest is given by  for

The transfer function of the system is:

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Q#28 Laplace Transform GATE EC 2005 (Set 1) MCQ +2 marks -0.66 marks

In what range should Re(s) remain so that the Laplace transform of the function  exists?

Re(s)>a+2

Re(s)>a+7

Re(s)<2

Re(s)>a+5

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Q#29 Laplace Transform GATE EC 2004 (Set 1) MCQ +2 marks -0.66 marks

A system described by the following differential equation  is initially at rest.

For input x(t) =2u(t), the output y(t) is

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Q#30 Laplace Transform GATE EC 2004 (Set 1) MCQ +2 marks -0.66 marks

A causal system having the transfer function  is excited with 10u(t). The time at which the output reaches 99% of its steady state value is

2.7 sec

2.5 sec

2.4 sec

2.1 sec

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Q#31 Laplace Transform GATE EC 2003 (Set 1) MCQ +1 mark -0.33 marks

The Laplace transform of i(t) is given by As, the value of i(t) tends to  

0

1

2

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Q#32 Laplace Transform GATE EC 2002 (Set 1) MCQ +2 marks -0.66 marks

The Laplace transform of a continuous-time signal x(t) is . If the Fourier transform of this signal exists, then x(t) is

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Q#33 Laplace Transform GATE EC 2001 (Set 1) MCQ +1 mark -0.33 marks

The transfer function of a system is given by. The impulse response of the system is: (* denotes convolution, and U(t) is unit step function)

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Q#34 Laplace Transform GATE EC 2000 (Set 1) MCQ +1 mark -0.33 marks

Given that , , .  is

None of the above

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Q#35 Laplace Transform GATE EC 2000 (Set 1) MCQ +2 marks -0.66 marks

A linear time invariant system has an impulse response, . If the initial conditions are zero and the input is, the output for  is

None of the above

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Q#36 Laplace Transform GATE EC 2000 (Set 1) MSQ +2 marks -0 marks

For the linear, time invariant system whose block diagram is shown in Figure (a), with input x(t) and output y(t),

(a) Find the transfer function.

(b) For the step response of the system [i.e. find y(t) when x(t) is a unit step function and the initial conditions are zero]

(c) Find y(t), if x(t) is as shown in Figure (b), and the initial conditions are zero.

Figure (a)

Figure (b)

30.jpg

(a) \(\scriptstyle {H(s) = \frac{1}{s^2 + 4s + 3}}\)

(b) \(\scriptstyle y(t) = \left[ \frac{1}{3} - \frac{e^{-t}}{2} + \frac{e^{-3t}}{6} \right] u(t)\)

(c) \(\scriptstyle {y(t) = \left\{ \left[ \frac{1}{3} - \frac{e^{-(t-1)}}{2} + \frac{e^{-3(t-1)}}{6} \right] u(t-1) - \left[ \frac{1}{3} - \frac{e^{-(t-2)}}{2} + \frac{e^{-3(t-2)}}{6} \right] u(t-2) \right\}}\)

(c) \(\scriptstyle {y(t) = \left\{ \left[ \frac{1}{3} + \frac{e^{-(t-1)}}{2} + \frac{e^{-3(t-1)}}{6} \right] u(t-1) - \left[ \frac{1}{3} - \frac{e^{-(t-2)}}{2} + \frac{e^{-3(t-2)}}{9} \right] u(t-2) \right\}}\)

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Q#37 Laplace Transform GATE EC 1999 (Set 1) MCQ +1 mark -0.33 marks

If , then  is equal to

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Q#38 Laplace Transform GATE EC 1998 (Set 1) MCQ +1 mark -0.33 marks

If , then the value of

Cannot be determined

Is zero

Is unity

is infinite

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Q#39 Laplace Transform GATE EC 1998 (Set 1) MCQ +1 mark -0.33 marks

The unit impulse response of a linear time invariant system is the unit step function u(t). For , the response of the system to an excitation ,  will be

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Q#40 Laplace Transform GATE EC 1997 (Set 1) MCQ +1 mark -0.33 marks

The Laplace Transform of $\scriptstyle e^{\alpha t} \cos(\alpha t)$ is equal to

None of these

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Q#41 Laplace Transform GATE EC 1996 (Set 1) MCQ +2 marks -0.66 marks

The inverse Laplace transform of the function  is

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Q#42 Laplace Transform GATE EC 1995 (Set 1) MCQ +1 mark -0.33 marks

If  then  and  are given by

[Note: ‘L’ stand for ‘Laplace’ Transform of’]

0, 2 respectively

2, 0 respectively

0, 1 respectively

2/5, 0 respectively

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Q#43 Laplace Transform GATE EC 1995 (Set 1) MCQ +1 mark -0 marks

Match the following

(A) Fourier transform of a Gaussian function

(B) Convolution of a rectangular pulse with itself

(C) Current through an inductor for a step input voltage  

(1) Gaussian function

(2) Rectangular pulse

(3) Triangular pulse

(4) Ramp function

(5) Zero

(A) => (1)
(B) => (3)
(C) => (4)

(A) => (2)
(B) => (3)
(C) => (4)

(A) => (2)
(B) => (3)
(C) => (5)

(A) => (5)
(B) => (2)
(C) => (4)

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Q#44 Laplace Transform GATE EC 1994 (Set 1) MCQ +1 mark -0.33 marks

The Laplace transform of a unit ramp function starting at , is

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Q#45 Laplace Transform GATE EC 1994 (Set 1) NAT +1 mark -0 marks

If G(s) is a stable transfer function, then  is always a stable transfer function
(True=1,False=0)

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Q#46 Laplace Transform GATE EC 1993 (Set 1) MCQ +2 marks -0.66 marks

If  then  is given by

Zero

undefined

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Q#47 Laplace Transform GATE EC 1991 (Set 1) MCQ +1 mark -0.33 marks

The voltage across an impedance in a network is , where ,  are the Laplace transforms of the corresponding time function v(t), z(t) and i(t). The voltage v(t) is:

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