91.
Consider the following statements for a.c. series motors:
1. The rotor is designed so that its R/X ratio is small.
2. dT/dω < 0 where T and ω are torque and speed respectively.
3. The reference and control voltages should be in phase quadrature, but their magnitudes need not be equal.
Which of the statement given above are correct?

92.
Which one of the following is NOT a correct statement about the state-space model of a physical system?

93.
A certain control system is represented by the following differential equation. Its transfer function would be $$\frac{{{d^2}y}}{{d{t^2}}} + \frac{{dy}}{{dt}} + 3y = \frac{{dx}}{{dt}} + 2x$$

96.
Which of the following rotors are used in a two-phase ac servomotor?
1. Solid iron motor
2. Squirrel cage rotor
3. Drag cup rotor
Select the correct answer using the options given below:

97.
A system with the transfer function $$\frac{{Y\left( s \right)}}{{X\left( s \right)}} = \frac{s}{{s + p}}$$   has an output $$y\left( t \right) = \cos \left( {2t - \frac{\pi }{3}} \right)$$    for the input signal $$x\left( t \right) = p\cos \left( {2t - \frac{\pi }{2}} \right).$$     Then, the system parameter 'p' is

98.
In case of d.c. servomotor, the back-emf is equivalent to an "electric friction" which tends to:

100.
Despite the presence of negative feedback, control system still have problems of instability because of

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