A resistance spot-welding operation is performed on twopieces of 1.5 mm thick sheet steel using 12000 amps current for a duration of 0.20 second. The electrodes are 6 mm in
diameter at the contacting surfaces. Resistance is assumed to be 0.0001 ohms and the resulting weld nugget is 6 mm in diameter and 2.5 mm thick. The unit melting energy for the metal is 12 J/mm$$^3$$. What portion of heat generated was used to form the weld?