physics
posted by Mary .
A cylindrical copper cable carries a current of 1260 A. There is a potential difference of 1.6 102 V between two points on the cable that are 0.32 m apart. What is the radius of the cable?

The current and potential difference together tell you the resistance R = V/I = 1.27*10^5 Ohms
1.27*10^5 = (rho)*L/A
where rho = the resisitivity of copper, in ohmm, and A = the crosssectional area (m^2), which is pi R^2
Solve for R. You will have to look up rho of copper.