A rectangular block is subjected to a shear stress of 40 N/mm2. The size of the block is 100 mm × 80 mm × 50 mm. If the modulus of rigidity of the material is 1 × 105 N/mm2, then the strain energy stored will be
1
3.2 N-m
2
2.4 N-m
3
1.8 N-m
4
1.6 N-m