A circular rod which tapers uniformly from 30 mm diameter to 20 mm diameter and another rectangular bar of constant thickness 5 mm and uniformly tapering in width from 20 mm to 10 mm. The length and applied axial load are same for both the bars, the ratio of the elongation in the respective bar is ? (Take E=2×105N/mm2 for both material)
Extension of uniformly tapering circular rod due to axial load=
=4PLπED1D2
=4×P×Lπ×2×105×30×20
Extension of uniformly tapering rectangular bar
=PLEt(B1−B2)loge(B1B2)
=PL2×105×5(20−10)×loge(2010)
Required ratio =4PLπE×30×20PLEt(20−10)loge(2)
=4π×30×20×5×10loge(2)=0.153