Density of rubber is $​d$​. $​ A$​ thick rubber cord of length $​L$​ and cross-section area $​A$​ undergoes elongation under its own weight on suspending it. This elongation is proportional to

A steel wire of length $4.7\; m$ and cross-sectional area $3.0 \times 10^{-5}\; m ^{2}$ stretches by the same amount as a copper wire of length $3.5\; m$ and cross-sectional area of $4.0 \times 10^{-5} \;m ^{2}$ under a given load. What is the ratio of the Young's modulus of steel to that of copper?

The proportional limit of steel is $8 \times 10^8 \,N / m ^2$ and its Young's modulus is $2 \times 10^{11} \,N / m ^2$. The maximum elongation, a one metre long steel wire can be given without exceeding the elastic limit is …… $mm$

There are two wires of same material and same length while the diameter of second wire is $2$ times the diameter of first wire, then ratio of extension produced in the wires by applying same load will be 

A rod of length $L$ at room temperature and uniform area of cross section $A$, is made of a metal having coefficient of linear expansion $\alpha {/^o}C$. It is observed that an external compressive force $F$, is applied on each of its ends, prevents any change in the length of the rod, when it temperature rises by $\Delta \,TK$. Young’s modulus, $Y$, for this metal is