What is the relation obeyed by the angles of contact $$\theta_1, \theta_2$$ and $$\theta_3$$ of 3 liquids of different densities $$P_1, P_2$$ and $$P_3$$ respectively $$(\mathrm{P}_1 < \mathrm{P}_2 < \mathrm{P}_3$$) when they rise to the same capillary height in 3 identical capillaries and having nearly same surface tension $$\mathrm{T}$$ ?

64 rain drops of the same radius are falling through air with a steady velocity of $$0.5 \mathrm{~cm} \mathrm{~s}^{-1}$$. If the drops coalesce, the terminal velocity would be

A block of wood floats in water with $$(4 / 5)$$ th of its volume submerged. If the same block just floats in a liquid, the density of the liquid is (in $$\mathrm{kgm}^{-3}$$)

A balloon with mass $m$ is descending down with an acceleration $$a$$ (where, $$a < g$$ ). How much mass should be removed from it so that it starts moving up with an acceleration $$a$$ ?