Consider the structural system shown in the figure under the action of weight $$W.$$ All the joints are hinged. The properties of the members in terms of length $$(L),$$ area $$(A)$$ and the modulus of elasticity $$(E)$$ are also given in the figure. Let $$L,A$$ and $$E$$ be $$1$$ $$m,$$ $$0.05$$ $${m^2}$$ and $$30 \times {10^6}\,\,N/{m^2},\,\,$$ respectively, and $$W$$ be $$100$$ $$kN.$$

Which one of the following sets gives the correct values of the force, stress and change in length of the horizontal member $$QR$$?

For the $$2D$$ truss with the applied loads shown below, the strain energy in the member $$XY$$ is _______________ $$kN$$-$$m$$. For member $$XY$$, assume $$AE = 30$$ $$kN,$$ where $$A$$ is cross-section area and $$E$$ is the modulus of elasticity.

For the truss shown below, the member $$PQ$$ is short by $$3$$ $$mm.$$ The magnitude of vertical displacement of joint $$R$$ (in $$mm$$) is ______________________