For a tall column resting on the ground, axial stress develops due to the columns weight. (a) Derive the stress as a function of position z measured from the bottom of the column, and the total contraction of the column. Express the results in terms of the column cross-sectional area A, mass density p, modulus E, and height H. (b) Evaluate the maximum stress and total contraction of height for a case of a hollow steel tower that is 70 m tall and has a 3.4 m outer diameter and wall thickness of 25 mm. Density and Youngs modulus of steel is given by 7850 kg/m3 and 200 GPa.