$A$ stretched wire of a material whose Young's modulus $Y = 2 \times 10^{11} \ Nm^{-2}$ has Poisson's ratio $\sigma = 0.25$. Its lateral strain is $\varepsilon_l = 10^{-3}$. The elastic energy density of the wire is:

The lengths of four wires $A, B, C$ and $D$ made of the same material are $1 \,m, 2 \,m, 3 \,m$ and $4 \,m$ respectively. The radii of the wires $A, B, C$ and $D$ are $0.2 \,mm, 0.4 \,mm, 0.6 \,mm$ and $0.8 \,mm$ respectively. For the same applied tension, the elongation is more in which wire?

$A$ metal wire with circular cross-section and length $1 \,m$ is pulled with a tensile force of $1000 \,N$ on each side. For the wire to be stretched not more than $0.25 \,cm$, the minimum diameter of the wire required is (Young's modulus of the metal $= 10^{11} \,Pa$, take $\sqrt{\pi} = 1.77$). (in $\,mm$)

$(a)$ $A$ steel wire of mass $\mu$ per unit length with a circular cross-section has a radius of $0.1\,cm$. The wire is of length $10\,m$ when measured lying horizontal and hangs from a hook on the wall. $A$ mass of $25\,kg$ is hung from the free end of the wire. Assuming the wire to be uniform and lateral strains $\ll$ longitudinal strains,find the extension in the length of the wire. The density of steel is $7860\,kg/m^3$ and Young's modulus $Y = 2 \times 10^{11}\,N/m^2$.
$(b)$ If the yield strength of steel is $2.5 \times 10^8\,N/m^2$,what is the maximum weight that can be hung at the lower end of the wire?

If Young's modulus for a material is zero,then the state of material should be

$A$ steel rod of diameter $1\,cm$ is clamped firmly at each end when its temperature is $25\,^{\circ}C$ so that it cannot contract on cooling. The tension in the rod at $0\,^{\circ}C$ is approximately ......... $N$ $(\alpha = 10^{-5}/\,^{\circ}C, Y = 2 \times 10^{11}\,N/m^2)$