$A$ wire of length $L$ and radius $r$ is clamped at one end. If its other end is pulled by a force $F$,its length increases by $l$. If the radius of the wire and the applied force both are reduced to half of their original values keeping original length constant,the increase in length will become.

The pressure that has to be applied to the ends of a steel wire of length $10 \ cm$ to keep its length constant when its temperature is raised by $100 \ ^\circ C$ is: (For steel,Young's modulus $Y = 2 \times 10^{11} \ N/m^2$ and coefficient of thermal expansion $\alpha = 1.1 \times 10^{-5} \ K^{-1}$)

Two uniform rods $AB$ and $BC$ have Young's moduli $1.2 \times 10^{11} \, N/m^2$ and $1.5 \times 10^{11} \, N/m^2$ respectively. If the coefficient of linear expansion of $AB$ is $1.5 \times 10^{-5} /^{\circ}C$ and both have equal area of cross-section,then the coefficient of linear expansion of $BC$,for which there is no shift of the junction at all temperatures,is ............. $\times 10^{-5} /^{\circ}C$.

$A$ copper wire and an aluminium wire have lengths in the ratio $5: 2$, diameters in the ratio $4: 3$ and forces applied in the ratio $4: 5$. Find the ratio of increase in length of the copper wire to that of the aluminium wire. (Given: $Y_{Cu} = 1.1 \times 10^{11} \text{ Nm}^{-2}$, $Y_{Al} = 0.7 \times 10^{11} \text{ Nm}^{-2}$)

Increase in length of a wire is $1 \, mm$ when suspended by a weight. If the same weight is suspended on a wire of double its length and double its radius,the increase in length will be ........ $mm$.

$A$ steel wire of length $L$ at $40^{\circ}C$ is suspended from the ceiling and then a mass $m$ is hung from its free end. The wire is cooled down from $40^{\circ}C$ to $30^{\circ}C$ to regain its original length $L$. The coefficient of linear thermal expansion of the steel is $10^{-5} /^{\circ}C$,Young's modulus of steel is $10^{11} N/m^2$,and the radius of the wire is $1 mm$. Assume that $L \gg$ diameter of the wire. Then the value of $m$ in $kg$ is nearly: