Let a steel bar of length $l$,breadth $b$,and depth $d$ be loaded at the centre by a load $W$. Then the sag of bending of the beam is ($Y =$ Young's modulus of the material of steel).

$A$ pendulum made of a uniform wire of cross-sectional area $A$ has a time period $T$. When an additional mass $M$ is added to its bob,the time period changes to $T_M$. If the Young's modulus of the material of the wire is $Y$,then $\frac{1}{Y}$ is equal to ($g$ = gravitational acceleration).

$A$ steel rod of length $1\,m$ and cross-sectional area $10^{-4}\,m^2$ is heated from $0^{\circ}C$ to $200^{\circ}C$ without being allowed to extend or bend. The compressive force produced in the rod is $........\times 10^4\,N$. (Given: Young's modulus of steel $Y = 2 \times 10^{11}\,N/m^2$,coefficient of linear expansion $\alpha = 10^{-5}\,K^{-1}$)

$A$ wooden wheel of radius $R$ is made of two semicircular parts (see figure). The two parts are held together by a ring made of a metal strip of cross-sectional area $S$ and length $L$. $L$ is slightly less than $2\pi R$. To fit the ring on the wheel,it is heated so that its temperature rises by $\Delta T$ and it just slips over the wheel. As it cools down to the surrounding temperature,it presses the semicircular parts together. If the coefficient of linear expansion of the metal is $\alpha$,and its Young's modulus is $Y$,the force that one part of the wheel applies on the other part is:

The unit of Young's modulus is

The ratio of the areas of cross-sections of three wires is $1:2:3$ and the ratio of the Young's moduli of their materials is $3:2:1$. If the three wires are of the same length and the same stretching force is applied to the three wires, then the ratio of the elongations of the three wires is