A rod of length 2 m is at a temperature of `20^@` C. find the free expansion of the rod, if the temperature is increased to `50^@`C, then find stress produced when the rod is (i) fully prevented to expand, (ii) permitted to expand by 0.4mm. `Y=2xx10^(11)N//m^(2), alpha=15xx10^(-6//^(@))C`.