2c) the only thing that has changed is the diameter, so only A changes (i guess that means current would too, dunno if it means both sides)
5a) you don't need to consider voltage - it give you a power, and a time, multiply them.
b) you know the energy transferred. divide it by the SHC and the mass (in kg). this would be the change in temp caused. to find the final temp add it to the room temp at the start.
c) some heat transferred to surroundings