Question

Two cylindrical vessels fitted with pistons A and B of area of cross section 8cm^2 and 320cm^2 respectively are joined at their bottom by a tube and they are completely filled with water. Find pressure on pistons.........

Answer 1

The diagram is missing here. In the diagram the arrangement would be clearer.

The pistons are exposed to the atmosphere. So atmospheric pressure acts on them. It is equal to 1.013 * 10⁵ Pa or N/m² or 1.013 * 10 dynes/cm²

As the pistons are both in static equilibrium, the pressure from the water is equal to the atmospheric pressure. So pistons are balanced. We assume that the pistons are weightless. (otherwise we need to add their weight to the pressure/thrust).

As the two cylindrical vessels are connected, water flows between them to equalize pressure at the same height or altitude. Thrust force is the force acting on the piston perpendicular to the surface area.

Pressure by water on Piston A or piston B = 10.13 dynes/cm²

Thrust force
= pressure * area of cross section
= 10.13 * 8 = 81.04 dynes for Piston A
and
= 10.13 * 320 = 3, 241.60 dynes for piston B
(1 dyne = 10⁻⁵ N)