What is the work done in stretching a uniform metal wire of length from 2 m to 2.004 m with an area of cross-section $10^{-6} \mathrm{~m}^2$ ?

[Young's modulus of the wire $=2 \times 10^{11} \mathrm{~N} / \mathrm{m}^2$ ]

A wide cylindrical vessel 50 cm in height is filled with water and rests on a table. Assuming the viscosity to be negligible. Find at what height from the bottom of the vessel a small hole should be made for the water jet coming out of it to hit the surface of the table at the maximum horizontal distance from the vessel

A spherical drop of radius $r$ is divided into 8 equal droplets. If the surface tension is $S$, then the work done in the process will be

A circular copper ring at $30^{\circ} \mathrm{C}$ has a hole with an area of $9.98 \mathrm{~cm}^2$. It is made to slip onto a steel rod of cross-sectional area of $10 \mathrm{~cm}^2$, by raising the temperature of both ring and rod simultaneously by an amount $\Delta T$. If the coefficient of linear expansion of copper and steel are $17 \times 10^{-6} \rho \mathrm{C}$ and $11 \times 10^{-6} \rho \mathrm{C}$, then minimum value of $\Delta T$ should be