Halliday, Resnick & Walker — Current and Resistance: Problem 42

42 Copper and aluminum are being considered for a high-voltage transmission line that must carry a current of 50.0 A. The resistance per unit length is to be 0.150 \(\Omega\)/km. The densities of copper and aluminum are 8960 and 2600 \(\text{kg/m}^3\), respectively. Compute (a) the magnitude J of the current density and (b) the mass per unit length \(\lambda\) for a copper cable and (c) J and (d) \(\lambda\) for an aluminum cable.