Question Details

An LTI system is shown in the figure where G(s) = 100/(s2+0.1s+100) The steady state output of the system, to the input r(t) , is given as y(t)= a+bsin(10t+ θ). The values of ‘ a ’ and ‘b ’ will be

Options

A

a = 100, b = 1

B

a = 10, b = 1

C

a = 1, b = 10

D

a = 1, b = 100

Show Answer

Correct Answer :

Option C

a = 1, b = 10

Solution :

The correct option is a = 1, b = 10.

Analysis of the Given System:
From the provided block diagram, we see that the input signal is:
r(t)=1+0.1sin(10t)
And the transfer function of the LTI system is:
G(s)=100s2+0.1s+100

The steady-state output of the system y(t) can be calculated by applying the principle of superposition to the two components of the input signal r(t): a DC component and a sinusoidal component.

Step 1: Finding the DC Component of the Output (a)
The DC component of the input is rdc(t)=1, which corresponds to a frequency of ω=0 rad/s (or s=0).
Substituting s=0 into the transfer function:
G(0)=10002+0.1(0)+100=100100=1
Therefore, the steady-state DC output a is:
a=1×G(0)=1×1=1

Step 2: Finding the Sinusoidal Component of the Output (b)
The sinusoidal component of the input is rac(t)=0.1sin(10t), with a frequency of ω=10 rad/s.
We substitute s=jω=j10 into the transfer function:
G(j10)=100(j10)2+0.1(j)+100
Since j2=-1:
G(j10)=100-100+j1+100=100j1=-j100
The magnitude of the transfer function at ω=10 rad/s is:
|G(j10)|=100
The amplitude of the steady-state sinusoidal output b is given by multiplying the input amplitude by the magnitude of G(j10):
b=0.1×|G(j10)|=0.1×100=10

Conclusion:
Matching with the standard steady-state output form y(t)=a+bsin(10t+θ), we have:
a=1 and b=10.

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