A steel tube of 30 mm external diameter and 20mm internal diameter encloses a copper rod of 15mm diameter to which it is rigidly joined at each end. If at a temperature of 10^o C, there is no longitudinal stress, evaluate the stresses in the rod and the tube when the temperature is raised to 200^o C. Take E for steel and copper are 2.1 x 10⁵ N/mm² and 1x 10⁵ N/mm² respectively. The value of coefficient of linear expansion for steel and copper is given as 11 x 10^-6 per degree C and 18 x 10^-6 per degree C respectively.