Two flat copper sheets $($each $1\mathrm{.}0$ mm thick$)$ are being spot welded by the use of a current of $7000$ A and a current flow time of $0\mathrm{.}1$ s$.$ The electrodes are $4$ mm in diameter.$$ Estimate the heat generated in the weld zone assuming the resistance is $100$ micro$-$Ohms.$$ Assuming the volume of the weld nugget is $30$ cubic millimeters, how much of that heat is required to melt the nugget?