As, we can determine the response of the system by its 'impulse response' then why we use 'step response' and 'ramp response'. Is there any difference between all these response?
Like the impulse response, the step and ramp responses describe an LTI-system. There are situations when the step response or the ramp response describe what we want to know about the system more directly than the impulse response. When the input to a system is a piece-wise constant function of time, the transitions are well described by the step response. It gives quite directly information about overshoot and settling time.