A vertical right circular cylindrical tank has height h=8 feet high and diameter d=6 feet. It is full of kerosene weighing 50 pounds per cubic feet. How much work (W) does it take to pump all of the kerosene from the tank to an outlet which is at the level of the top of the tank?

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Answer:

The work done to  pump all of the kerosene from the tank to an outlet is [tex]W=45238.9\: J[/tex]  

Step-by-step explanation:

The work is defined by:

[tex]W=\int dFdx[/tex] (1)    

The force here will be the product between the volume and the kerosene weighing, so we have :

[tex]dF=\pi R^{2}dy*50[/tex]

This force will be in-lbs.

Where R is the radius (3 feet)                    

Then using (1), we have:

[tex]W=\int \pi R^{2}dy*50(8-y)[/tex]  

Here 8-y is a distance at some point of the tank. Now, to get the work done from the base to the top of the tank we will need to take integral from 0 to 8 feet.

[tex]W=\int_{0}^{8} \pi 3^{2}dy*50(8-y)[/tex]

[tex]W=450\pi \int_{0}^{8}dy(8-y)[/tex]

[tex]W=450\pi(\int_{0}^{8} 8dy-\int_{0}^{8} ydy)[/tex]

[tex]W=450\pi(8y|_{0}^{8} -\frac{y^{2}}{2}|_{0}^{8})[/tex]  

[tex]W=450\pi(8*8 -\frac{8^{2}}{2})[/tex]

[tex]W=450\pi(64 -\frac{64}{2})[/tex]

Therefore, the work done to  pump all of the kerosene from the tank to an outlet is [tex]W=45238.9\: J[/tex]  

I hope it helps you!  

The work taken to pump all of the kerosene from the tank is 25446.6 pound-force-feet.

Procedure - Work needed to pump out a fluid in a right circular tank

Let suppose that kerosene has an uniform density ([tex]\rho[/tex]), in pounds per cubic feet, and the pumping process occurs at steady state, which means that work ([tex]W[/tex]), in pound-force-feet, needed is equal to the gravitational potential energy ([tex]U[/tex]), in pound-force-feet, of the fluid in the right circular tank.

By definition of work and the work-energy theorem we have the following line integral:

[tex]W = \oint \vec F \,\bullet\,d \vec s [/tex]

[tex]W = \frac{\rho\cdot A\cdot g}{g_{c}} \int \limits_{0}^{h} s\,ds[/tex] (1)

The solution of this integral is:

[tex]W = \frac{\rho\cdot A\cdot g\cdot h^{2}}{2\cdot g_{c}} [/tex] (1b)

Where:

  • [tex]\rho[/tex] - Density of the kerosene, in pounds-mass per cubic feet.
  • [tex]A[/tex] - Area of the transversal section of the right circular cylindrical tank, in square feet.
  • [tex]g[/tex] - Gravitational acceleration, in feet per square second.
  • [tex]h[/tex] - Height of the tank, in feet.
  • [tex]g_{c}[/tex] - Conversion factor, in pound-mass-feet per square second per pound-force.

The area of the transversal section of the right circular cylindrical tank is determined by the following expression:

[tex]A = \frac{\pi\cdot D^{2}}{4} [/tex] (2)

Where [tex]D[/tex] is the diameter of the tank, in feet.

If we know that [tex]D = 6\,ft[/tex], [tex]\rho = 50\,\frac{lbm}{ft^{3}} [/tex], [tex]g = 32.174\,\frac{ft}{s^{2}} [/tex], [tex]h = 6\,ft[/tex] and [tex]g_{c} = 32.174\,\frac{\frac{lbm\cdot ft}{s^{2}} }{lbf} [/tex], then the work needed to pump all of the kerosene is:

[tex]A = \frac{\pi\cdot (6\,ft)^{2}}{4} [/tex]

[tex]A \approx 28.274\,ft^{2}[/tex]

[tex]W = \frac{\left(50\,\frac{lbm}{ft^{3}} \right)\cdot (28.274\,ft^{2})\cdot \left(32.174\,\frac{ft}{s^{2}} \right)\cdot (6\,ft)^{2}}{2\cdot \left(32.174\,\frac{\frac{lbm\cdot ft}{s^{2}} }{lbf} \right)} [/tex]

[tex]W = 25446.6\,lbf\cdot ft[/tex]

The work taken to pump all of the kerosene from the tank is 25446.6 pound-force-feet. [tex]\blacksquare[/tex]

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