A mass of 5.0 kg is hung from a copper wire of 5 mm diameter and 2 m in length. Calculate the extension produced. What should be the minimum. diameter of the wire, so that its elastic limit is not exceeded? Elastic limit for copper=`1.5 x 10^ 9 dyne cm^-2` and Y for copper-1.1 x10^12 dyne cm^2.