A disc of radius 0.4 m and mass 1 kg rotates about an axis passing through its centre and perpendicular to its plane. The angular acceleration is 10 rad/s$^2$. The tangential force applied to the rim of the disc is

A body is projected vertically from earth's surface of radius R with velocity equal to half the escape velocity. The maximum height reached by the body is

Two small drops of liquid of same radius coalesce to form a big drop. The ratio of the total surface energies after and before the change is

Three liquids have same surface tension and have densities $\rho_1, \rho_2$ and $\rho_3$ $(\rho_1 > \rho_2 > \rho_3)$. In three identical capillaries rise of liquid is same. The corresponding angles of contact $\theta_1, \theta_2$ and $\theta_3$ are related as