Bernoulli's theorem is based on the principle of conservation of

Water flows through a frictionless duct with a cross-section varying as shown in figure. Pressure P at points along the axis is represented by: 

The figure shows a soap film in which a closed elastic thread is lying. The film inside the thread is pricked. Now, the sliding wire is moved out so that the surface area increases. The radius of the circle formed by elastic thread will,

A $20\mathrm{cm}$ long capillary tube is dipped vertically in water and the liquid rises upto $10\mathrm{cm}.$ If the entire system is kept in a freely falling platform, the length of water column in the tube will be