An ideal fluid of density 800 kgm^$$-$$3, flows smoothly through a bent pipe (as shown in figure) that tapers in cross-sectional area from a to $${a \over 2}$$. The pressure difference between the wide and narrow sections of pipe is 4100 Pa. At wider section, the velocity of fluid is $${{\sqrt x } \over 6}$$ ms^$$-$$1 for x = ___________. (Given g = 10 ms^$$-$$2)

The velocity of upper layer of water in a river is 36 kmh^$$-$$1. Shearing stress between horizontal layers of water is 10^$$-$$3 Nm^$$-$$2. Depth of the river is __________ m. (Co-efficient of viscosity of water is 10^$$-$$2 Pa.s)

In an experiment to verify Newton's law of cooling, a graph is plotted between the temperature difference ($$\Delta$$T) of the water and surroundings and time as shown in figure. The initial temperature of water is taken as 80$$^\circ$$C. The value of t₂ as mentioned in the graph will be __________.