A spherical object is falling under gravity through a viscous fluid. The sphere attains the terminal velocity when

A piston of cross-sectional area $2.5 \times 10^{-2}\ \text{m}^2$ is used in a hydraulic lift to exert a force of $250\ \text{N}$ on water. The cross-sectional area of the other piston which supports a car of mass $3000\ \text{kg}$ is ($g = 9.8\ \text{m/s}^2$)

Two spherical black bodies of radii $R_1$ and $R_2$ having surface temperature $T_1$ and $T_2$ respectively, radiate the same power. The ratio of $R_1$ to $R_2$ will be

The ratio of thermal conductivity of two rods of different materials is $4:3$. The two rods have same area of cross-section and same thermal resistance. The lengths of rods are in the ratio