Each of three blocks $$\mathrm{P}, \mathrm{Q}$$ and $$\mathrm{R}$$ shown in figure has a mass of $$3 \mathrm{~kg}$$. Each of the wires $$\mathrm{A}$$ and $$\mathrm{B}$$ has cross-sectional area $$0.005 \mathrm{~cm}^2$$ and Young's modulus $$2 \times 10^{11} \mathrm{~N} \mathrm{~m}^{-2}$$. Neglecting friction, the longitudinal strain on wire $$B$$ is ________ $$\times 10^{-4}$$. (Take $$\mathrm{g}=10 \mathrm{~m} / \mathrm{s}^2$$)

Two metallic wires $$P$$ and $$Q$$ have same volume and are made up of same material. If their area of cross sections are in the ratio $$4: 1$$ and force $$F_1$$ is applied to $$P$$, an extension of $$\Delta l$$ is produced. The force which is required to produce same extension in $$Q$$ is $$\mathrm{F}_2$$.

The value of $$\frac{F_1}{F_2}$$ is _________.

In a test experiment on a model aeroplane in wind tunnel, the flow speeds on the upper and lower surfaces of the wings are $$70 \mathrm{~ms}^{-1}$$ and $$65 \mathrm{~ms}^{-1}$$ respectively. If the wing area is $$2 \mathrm{~m}^2$$, the lift of the wing is _________ $$N$$.

(Given density of air $$=1.2 \mathrm{~kg} \mathrm{~m}^{-3}$$)

The reading of pressure metre attached with a closed pipe is $$4.5 \times 10^4 \mathrm{~N} / \mathrm{m}^2$$. On opening the valve, water starts flowing and the reading of pressure metre falls to $$2.0 \times 10^4 \mathrm{~N} / \mathrm{m}^2$$. The velocity of water is found to be $$\sqrt{V} \mathrm{~m} / \mathrm{s}$$. The value of $$V$$ is _________.