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.

Two identical solid balls,one of ivory and the other of wet-clay,are dropped from the same height on the floor. Which one will rise to a greater height after striking the floor and why?

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 $g = 10 \, m/s^{2}$)

What is Elastic Moduli?

Explain with the illustration of cranes the applications of the elastic behaviour of materials.

Why do spring balances show wrong readings of weight after they have been used for a long time?