Fluid pressure (verification please)

[kieslingrc]

1. The water in a tank is at a gauge pressure of 267,018 Pa. If the bottom of the tank that has an area of 0.8 m2, what is the force on the bottom of the tank?



2. P=F/A; F=P*A



3. Converted Pa into 38.8psi for P (267,018/6890); Converted the Area into 103.7 in^2 (.8*10.8*12); Multiply [P*A] 38.8 * 103.7 = 4023.6 in lbs = 335.3 lbs of force. Did I do this right?

 

[LawrenceC]

The portion about the Paschals to PSI is pretty close but the area portion is wrong.

 

[kieslingrc]

We are to use all units in the book and to 1 decimal place rounded up so that's where I came up with the Pa conversion.

Hmmm, in my book, the conversion is 1m^2 = 10.8ft^2, so I converted the m - ft by multiplying it leaving 8.6ft^2. I had to get the units to be the same so converted ft^2 to in^2, multiplying it by 12. Where did I go wrong? Thanks in advance for your guidance.

 

[LawrenceC]

How many SQUARE inches in a SQUARE foot?

 

[kieslingrc]

gotcha, I needed to multiply by 144, not 12, right? But in that case, my numbers seem way too high.

 

[LawrenceC]

You have pressure of roughly 38 psi with an area of .8 m^2 which is about 1240 in^2. The force is large.

 

[kieslingrc]

So that leave me 48,275 psi, or 335.2 ft lb^2. The force is 112,359 lbs.

 

[LawrenceC]

No. Pressure times area is force. Why do you write psi for force? Force is pounds. Pressure is pounds per square inch.

The units work algebraically just like variables.

(lbs/in^2)X(in^2) = lbs

The pressure is 267018 Pa which is 38.73 lbs/in^2
The area is 0.8 m^2 which is 1240 in^2.

Multiply them!

 

[kieslingrc]

OK, I am totally confused. Let me start over.

The pascal conversion was fine, no need to work with that anymore. 38.8 lb/in^2
Area: [1m^2 = 10.8ft^2]; [10.8ft^2 = 1555.2 in^2] Convert the area 1555.2 * 0.8 = 1244.2in^2.
The force is 38.8 * 1244.2 = 48,275lbs

 

[LawrenceC]

That's it. You've got it now.

 

[kieslingrc]

Thanks Lawrence for helping me understand what I was doing wrong.