A homogenous bar of length L has weight W and links with a hanging block (weight G). The spring of spring constant k is unstretched when the bar is vertical (a=0). Note: Marks will not be awarded if a method other than virtual work or potential energy is used. (4.1) Demonstrate that the bar is equilibrium when α=0, independent of the exact weights of the bar and the block. DO NOT SOLVE for multiple solutions. (4.2) Show the criterion for the spring constant k, in order to let the equilibrium position a=0 stable. G