What is the amplitude of output signal in below circuit?
From the topology you can see this is a low pass filter.  I would start with getting some intuition of how this filter is going to behave, rather than trying to see what exactly happens at your frequency.  For frequencies well below the rolloff, you can approximate the capacitor as a open, and well above the rolloff as a short.  By computing the gain at the limits and looking at where the rolloff frequency is, you can draw out a Bode plot from inspection.

Then you can look at where your frequency of interest fits on that plot and get a quick idea of the gain.

That brings up another issue, which is that it's unclear what your frequency is since you haven't defined the units of T.  If T is in seconds, then the frequency is 1000 / (2&pi; s) = 160 Hz.