A 5.0 cm long straight piece of thread is kept on the surface of water. Find the force with which the surface on one side of the thread pulls it Surface tension of water = 0.076 N m^-1.

Estimate the change in the density of water in ocean at a depth of 400 m below the surface. The density of water at the surface 1030 kg m^-3 and the bulk modulus of water = 2 × 10⁹ N m^-2.

A steel plate of face area 4 cm² and thickness 0.5 cm is fixed rigidly at the lower surface. A tangential force of 10 N is applied on the upper surface. Find the lateral displacement of the upper surface with respect to the lower surface. Rigidity modulus of steel = 8.4 × 10¹⁰ N m^-2.

Find the excess pressure inside (a) a drop of mercury of radius 2 mm (b) a snap bubble of radius 4 mm and (c) an air bubble of radius 4 mm formed inside a tank of water. Surface tension of mercury, soap solution and water are 0.465 N m^-1, 0.03 N m^-1 and 0.076 N m^-1 respectively.

Consider a small surface area of 1 mm² at the top of a mercury drop of radius 4.0 mm. Find the force exerted on this area to) by the air above it (b) by the mercury below it and (c) by the mercury surface in contact with it. Atmospheric pressure = 1.0 × 10⁵ Pa and surface tension of mercury = 0.465 N m^-1. Neglect the effect of gravity. Assume all numbers to be exact.