Question

A control system whose step response is -0.5(1+e^-2t) is cascaded to another control block whose impulse response is e^-t. What is the transfer function of the cascaded combination?

(a) 1/(s+2)(s+1)

(b) 1/(s+1)s

(c) 1/(s+3)

(d) 0.5/(s+1)(s+2)

The question was asked in a job interview.

Query is from Transfer Functions topic in section Mathematical Models of Physical Systems of Control Systems

Answer 1

Right choice is (a) 1/(s+2)(s+1)

To elaborate: Solution: Laplace transform is the transformation that transforms the time domain into frequency domain and of both the cascaded systems are 1/(s+1)(s+2).