The viscous drag acting on a metal sphere of diameter $$1 \mathrm{~mm}$$, falling through a fluid of viscosity $$0.8 \mathrm{~Pa}$$ s with a velocity of $$2 \mathrm{~m} \mathrm{~s}^{-1}$$ is equal to :

The amount of energy required to form a soap bubble of radius $$2 \mathrm{~cm}$$ from a soap solution is nearly: (surface tension of soap solution $$=0.03 \mathrm{~N} \mathrm{~m}^{-1}$$ )

The venturi-meter works on :

Let a wire be suspended from the ceiling (rigid support) and stretched by a weight $$W$$ attached at its free end. The longitudinal stress at any point of cross-sectional area $$A$$ of the wire is :