A metallic bar of Young's modulus, $$0.5 \times 10^{11} \mathrm{~N} \mathrm{~m}^{-2}$$ and coefficient of linear thermal expansion $$10^{-5}{ }^{\circ} \mathrm{C}^{-1}$$, length $$1 \mathrm{~m}$$ and area of cross-section $$10^{-3} \mathrm{~m}^2$$ is heated from $$0^{\circ} \mathrm{C}$$ to $$100^{\circ} \mathrm{C}$$ without expansion or bending. The compressive force developed in it is :

The amount of elastic potential energy per unit volume (in SI unit) of a steel wire of length $$100 \mathrm{~cm}$$ to stretch it by $$1 \mathrm{~mm}$$ is (if Young's modulus of the wire $$=2.0 \times 10^{11} \mathrm{Nm}^{-2}$$ ) :

Which of the following statement is not true?

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 :