(a) Find the Laplace transform of f(t) = t^2 u(t - 3). (5%)

1. An aluminum bar AD (Fig. 1) has a crosssectional area of A = 250 mm2 and is loaded by forces P1 = 7560 N, P2 = 5340 N, and P3 = 5780 N. The lengths of the segments of the bar are a = 1525 mm, b = 610 mm, and c = 916 mm shown in Fig.1. Assuming that the modulus of elasticity E = 72 GPa, calculate the change in length of the bar. Does the bar elongate or shorten? (20%)