Question 1 It is desired to design a stiff cylindrical PV of internal diameter (ID) and length (L). Optional materials of construction are steel and aluminum. It is known that material stiffness is proportional to with modulus of elasticity of the material. Also, stiffness is proportional to the cube of material thickness. A designed steel cylindrical PV could have shell thickness of ts. For the elastic modulus of steel being three (3) times that of aluminum, and density of aluminum being one-third the density of steel, calculate the percentage increase or decrease in the cost of the PV for design of an equivalent stiff aluminum cylindrical PV of shell thickness ( tA) [10 marks] [Material cost: Aluminum, CA=$3.50/kg; Steel, CS=$2.35/kg ] Stress amplitude (a)ksi