Hello,
You are looking for the "energetic classification" of signals. Lookup the following concepts:
- Finite energy signals.
- Finite average power signals.
A signal can have infinite energy, but a finite average power (check your second equation for power of the Heaviside step (Is the limit of infinity/infinity really infinity, or is it something else?).
Also, check the way you defined u(t). Are you trying to define a gate/boxcar or a "true" Heaviside function (i.e : 0 ; t < 0 and 1 ; t > 0 ). Either way, your integral disagrees with your function.
Try to write your equations in a symbolic way first, then the numbers.