An annular disc of radius $r=10 \mathrm{cm}$ and $R=20 \mathrm{cm}$ is placed on a water surface, Calculate the force required to take away the plate from the surface of water. Surface tension of water $=0.07 \mathrm{N} {\mathrm{m}}^{-1}$

In figure $\left(a\right)$ given below shows a thin liquid film supporting a small weight equal to $5.0\times {10}^{-2} N$. What is the weight supported by a film of the same liquid at the same temperature in Figs. $\left(b\right)$ and $\left(c\right)$ ?

A circular ring has inner and outer radii equal to $r$ and $R$ respectively. Mass of the ring is $m$ It gently pulled out vertically from a water surface by a sensitive spring. When the spring is stretched $3.4 cm$ from its equilibrium position the ring is on verge of being pulled out from the water surface. If spring constant is $k$. Find the surface tension of water.

A glass plate of length $50 \mathrm{cm}$, breadth $40 \mathrm{cm}$ and thickness $5 \mathrm{cm}$ weighs $3 \mathrm{kg}$ in air. If it is held vertically with long side horizontal and the plate half immersed in a liquid, what will be its apparent weight? Surface tension of the liquid $=50\times {10}^{-2} \mathrm{N} {\mathrm{m}}^{-1}$