# Pressure 2 m deep in a tank full of water

• SpiffyPhysics
In summary, the question asks for the pressure on a surface 6 meters below the water level in a tank filled with water. The equation given is P=hdg, but it is not possible for the pressure to be 1.5 kPa at a depth of 2 meters using this equation. This could be due to the context or location of the problem, as well as the possibility of the fluid not being water. It is also suggested that the pressures given are gauge pressures and the tank is in an accelerating elevator.
SpiffyPhysics

## Homework Statement

In a tank full of water, the pressure on a surface 2 meters below the water level is
1.5 kPa. What is the pressure on a surface 6 meters below the water level?

## Homework Equations

Isn't this impossible? The equation given is P=hdg. (height of water column x density x 9.8m/s/s) and the density of water is 1.

## The Attempt at a Solution

So by that equation, the pressure 2 meters below would be P=2m x 1 x 9.8m/s/s = 19.6 kPa
and the pressure 6 meters below the surface would be P= 6m x 1 x 9.8m/s/s = 58.8 kPa

Am I misunderstanding something here?

SpiffyPhysics said:
The equation given is P=hdg.
This equation gives zero pressure at a height of 0. Possible, but it is a special case that does not have to be true. There is a more general formula. Alternatively, consider pressure differences only.

The planet is not specified. But then, neither is its atmospheric pressure, making the whole indeterminate.

I guess we can assume this happens at the surface of Earth. Atmospheric pressure does not influence the result (but we have to assume that 1.5 kPa are pressure relative to atmospheric pressure otherwise the described system cannot exist).

mfb said:
I guess we can assume this happens at the surface of Earth. Atmospheric pressure does not influence the result (but we have to assume that 1.5 kPa are pressure relative to atmospheric pressure otherwise the described system cannot exist).
But Spiffy's point is that the set up described is not possible under those conditions. The excess pressure would be more like 20kPa at 2m. That's why I brought up the possibility of a different context.

Excess pressure relative to the highest point in the tank, which can be below atmospheric pressure.

mfb said:
Excess pressure relative to the highest point in the tank, which can be below atmospheric pressure.
Sure, but it can't be negative. Even if the tank is under a vacuum the pressure at 2m will be far more than the question states.

Sometimes pressure is given relative to atmospheric pressure. I suggest to wait for SpiffyPhysics.

@SpiffyPhysics: Is this the full and exact problem statement?

mfb said:
Sometimes pressure is given relative to atmospheric pressure. I suggest to wait for SpiffyPhysics.

@SpiffyPhysics: Is this the full and exact problem statement?
Let the absolute pressure at the surface be P. On Earth, the pressure at 2m depth of water will be about P+20kPa, yes? What value of P is going to give a resulting pressure of a mere 1.5kPa?

The only interpretation that makes sense to me is a) this is not on Earth, and b) the pressures are relative to atmospheric, whatever that is.

haruspex said:
Let the absolute pressure at the surface be P. On Earth, the pressure at 2m depth of water will be about P+20kPa, yes? What value of P is going to give a resulting pressure of a mere 1.5kPa?

The only interpretation that makes sense to me is a) this is not on Earth,
Or the fluid is not water.

The pressures are gauge pressures and the tank is in an elevator.

ehild said:
Or the fluid is not water.
It says water.

TSny said:
The pressures are gauge pressures and the tank is in an elevator.
An accelerating elevator... Albert E says that might as well be a different planet.

## 1. What is the formula for calculating pressure at a specific depth in a tank of water?

The formula for calculating pressure at a specific depth in a tank of water is P = ρgh, where P is pressure, ρ is the density of water, g is the acceleration due to gravity, and h is the depth.

## 2. How does the pressure change as the depth increases in a tank of water?

The pressure increases as the depth increases in a tank of water. This is because the weight of the water above exerts more force on the lower layers of water, resulting in higher pressure.

## 3. What is the unit of measurement for pressure in a tank of water?

The unit of measurement for pressure in a tank of water is typically Pascal (Pa) or pounds per square inch (psi).

## 4. Does the shape or size of the tank affect the pressure at a specific depth?

No, the shape or size of the tank does not affect the pressure at a specific depth. The pressure is solely determined by the depth and density of the water.

## 5. How does the pressure at a depth of 2 meters compare to the pressure at the surface of the water in a tank?

The pressure at a depth of 2 meters will be greater than the pressure at the surface of the water in a tank. This is because the depth of 2 meters adds more weight and therefore more force on the lower layers of water, resulting in higher pressure.

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