A solid cylindrical bar of 5-mm diameter is slowly stretched from an initial length of 100 mm to a final length of 101 mm. The normal stress acting at the end of the bar varies according to s = E(x - x1)/x1 , where x is the position of the end of the bar, x1 is the initial length, and E is a material constant (Young's modulus). For E = 2 * 107 kPa, determine the work done on the bar (J).