A steel bar 8.0 ft long has a circular cross section of diameter d1 = 0.75 in. over one-half of its length and diameter d2 = 0.5 in. over the other half (see figure). The modulus of elasticity E = 30 × 106 psi.
(a) How much will the bar elongate under a tensile load P = 5000 lb?
(b) If the same volume of material is made into a bar of constant diameter d and length 8.0 ft, what will be the elongation under the same load P?

di 0.75 in. d d,-0.50 in. P 5000 lb 4.0 ft4.0 ft