A steel rod of dimensions 4 x 4cm is tightly fixed between two supports and is not allowed to expand. It is heated through 2°C. Thermal stress developed is ..... 10 N/m² (Y= 20 x101°N/m a = 18 x 10-6/°C)
1) 7.2
2) 2.7
3) 3.6
4) 0.72