First off, if "V1" is = 0V, everything is off . all your answers are 0( 0V or 0A) !
Now if V1 is some value of voltage (AC or DC) we can explain things better!
Note:
U1 pin 3 is tied to Ground, Thus V+ = 0V !
So by Definition of an "OP-AMP", at all times" V-" must be (or will be adjusted
by Vo to be) = 0V (Because V+ ≡ 0V, OP-AMPS require V+ ≡ V- ) !
So with this in mind just think of it as :
What ever voltage wave-form V1 generates, Vo "WILL" create a related wave
form that always Keeps V- ≡ V+ !
Also one practical point that new students miss is:
Now matter how you set the gain of an op-amp and what voltage you put on the
inputs. The voltage rails of the op-amp set the highest voltage you can
produce at Vo !
If U1 pin 7 = +15V & U1 Pin 4 = 0V(Ground)
Vo max will always be +15V !
Thus you "i3" can only be as great as "Vmax"/R3; where Vmax is :
(U1 pin 7 Voltage) - (U1 pin 4 Voltage) = Vmax