Physics · Mechanical Properties Of Fluids · NEET
No. P0 is simply the pressure acting on the top surface of the fluid. If the top is open to air, then P0 equals atmospheric pressure (about 1.01 x 10^5 Pa). But if the tank is sealed with gas pushing on top, or if you are measuring from a point that is already deep, P0 is the pressure at that reference top level. Always read the problem to see what sits on the surface.
h is the vertical depth of your point below the free surface of the fluid, not the total height of the container. If a tank is 5 m tall but filled only to 3 m, and your point is at the bottom, then h = 3 m. Only the fluid column above your point matters.
Pressure adds up like stacked layers. The surface already has pressure P0 pushing down. As you go deeper, the extra weight of the fluid column adds an extra pressure rho g h on top of P0. So the total is a sum, P0 + rho g h, not a product. The rho g h part is called gauge pressure (the extra above P0).
P is the absolute (total) pressure at that point. The term rho g h is only the extra pressure caused by the fluid column, called gauge pressure. Absolute pressure P = P0 + gauge pressure. If a question asks for gauge pressure, the answer is just rho g h and you do not add P0.
No. Pressure at a point depends only on depth h, density rho and g, not on the shape or the amount of water. A thin tube and a wide tank filled to the same height have the same bottom pressure. This is called the hydrostatic paradox.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
P = P0 + rho g h. Here P is the total pressure at depth h, P0 is the pressure on the top surface, rho is the fluid density, g is acceleration due to gravity, and h is the depth below the surface.
Use P0 = 1.01 x 10^5 Pa (about 1.013 x 10^5 Pa), which is roughly 1 atmosphere or 760 mm of mercury, when the fluid top is open to air.
Gauge pressure = rho g h = 1000 x 10 x 10 = 1.0 x 10^5 Pa (about 1 atm). Using g = 9.8 gives 0.98 x 10^5 Pa.
Absolute pressure P = P0 + rho g h = 1.01 x 10^5 + 1.0 x 10^5 = 2.01 x 10^5 Pa, roughly 2 atmospheres.
No. At a given depth, hydrostatic pressure is the same in all directions (up, down, sideways). Only depth, density and g decide its value.
