The bar ABC shown in the figure is loaded by a force P acting at end C and by a force Q acting at the midpoint B. The bar has constant axial rigidity EA.
(a) Determine the strain energy U1 of the bar when the force P acts alone (Q = 0).
(b) Determine the strain energy U2 when the force Q acts alone (P = 0).
(c) Determine the strain energy U3 when the forces P and Q act simultaneously upon the bar.

L/2 L2