Calculating the power lost per foot from “\$I^2R\$ losses"
What you have done is applied 115 volts across the 1 foot of copper cable.  This isn't what we are doing here.  What you need to find is the amount of current through the cable, but you obtain that by calculating from the power and the voltage.  Since P=EI, I will be P/E.  When you get done, you can also find I*R, and that will be the voltage dropped across the 1 foot of cable.