$($b$)$

Fig. $1\mathrm{.}13$When the vertical load $P$ in Fig. $1\mathrm{.}13$a is gradually applied at point $A,$ deflec$-$

thes Is proportional to load and the work done externally is $P\frac{}{2},$ where $$ is the

deflection of point $A.$ Using the fact that this external work must be stored in the

wires in the form of strain energy, calculate the deflection $.$ Assume that each wire

has the same cross$-$sectional area A and modulus of elasticity $E$ in tension. Ans.

$\frac{Pl}{AE}(\frac{1}{1+2co{s}^3})$