$A$ rod is placed on a smooth horizontal surface. What is the stress developed when the temperature is increased by $40\,^{\circ}C$?
$[\alpha = 5\, \times\, 10^{-5}\,^{\circ}C^{-1},\, Y = 5\, \times\, 10^{11}\, N/m^2]$

The breaking stress of aluminium is $7.5 \times 10^7 \,N m^{-2}$. The greatest length of aluminium wire that can hang vertically without breaking is ......... $\times 10^3 \,m$ (Density of aluminium is $2.7 \times 10^3 \,kg m^{-3}$ and $g = 9.8 \,m s^{-2}$)

The increase in length is $l$ of a wire of length $L$ by the longitudinal stress. Then the stress is proportional to

Wires $W_{1}$ and $W_{2}$ are made of the same material having a breaking stress of $1.25 \times 10^{9} \, N/m^{2}$. $W_{1}$ and $W_{2}$ have cross-sectional areas of $8 \times 10^{-7} \, m^{2}$ and $4 \times 10^{-7} \, m^{2}$,respectively. Masses of $20 \, kg$ and $10 \, kg$ hang from them as shown in the figure. The maximum mass $m$ that can be placed in the pan without breaking the wires is $..... \, kg$. (Use $g = 10 \, m/s^{2}$)

When a heavy weight is suspended from a metal wire and then removed,the wire does not regain its original length. Why?

If under an external force,a change in length $\Delta l$ occurs in a rod of original length $l$,then write the formula for longitudinal strain.