Math Problem Statement

A fuel oil tank is an upright cylinder, buried so that its circular top is 10 feet beneath ground level. The tank has a radius of 8 feet and is 24 feet high, although the current oil level is only 23 feet deep. Calculate the work required to pump all of the oil to the surface. Oil weighs 50lb/ft^3 . Work =

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Solution

To calculate the work required to pump all of the oil to the surface, we will use the formula for work in the context of fluid mechanics:

W=abF(y)dyW = \int_{a}^{b} F(y) \, dy

Where:

  • WW is the total work required to pump the oil.
  • F(y)F(y) is the force exerted at a given height yy.
  • aa and bb are the limits of integration, in this case, the range of oil depth.

Step-by-Step Calculation

  1. Volume of the tank at a given height:
    The tank is a cylinder, and the volume of a thin slice of oil at height yy (where yy is the distance from the bottom of the tank) is given by the area of the cross-section times the thickness of the slice. The cross-sectional area is constant and equals the area of a circle:

    A=πr2=π×(8)2=64π square feet.A = \pi r^2 = \pi \times (8)^2 = 64\pi \text{ square feet}.

  2. Force due to the weight of the oil:
    The weight of the oil in a thin slice at height yy (with thickness dydy) is:

    dF=(weight density)×(volume of the slice)=50×64πdy=3200πdy pounds.dF = \text{(weight density)} \times \text{(volume of the slice)} = 50 \times 64\pi \, dy = 3200\pi \, dy \text{ pounds}.

  3. Distance to pump the oil:
    The distance that a slice of oil at height yy must be pumped to the surface is 10+24y=34y10 + 24 - y = 34 - y feet, because the top of the tank is 10 feet below ground level, and the height of the oil column is yy.

  4. Work for a slice:
    The work to pump this slice to the surface is the force dFdF times the distance to the surface:

    dW=(3200πdy)×(34y).dW = (3200\pi \, dy) \times (34 - y).

  5. Total work:
    Now, to find the total work, we integrate from y=0y = 0 to y=23y = 23 (since the oil level is 23 feet deep):

    W=0233200π(34y)dy.W = \int_0^{23} 3200\pi (34 - y) \, dy.

Step-by-Step Integration

Let’s carry out the integration:

W=3200π023(34y)dy.W = 3200\pi \int_0^{23} (34 - y) \, dy.

First, we expand the integrand:

W=3200π[02334dy023ydy].W = 3200\pi \left[ \int_0^{23} 34 \, dy - \int_0^{23} y \, dy \right].

Now we solve each part:

  • 02334dy=34y023=34×23=782\int_0^{23} 34 \, dy = 34y \Big|_0^{23} = 34 \times 23 = 782,
  • 023ydy=y22023=2322=5292=264.5\int_0^{23} y \, dy = \frac{y^2}{2} \Big|_0^{23} = \frac{23^2}{2} = \frac{529}{2} = 264.5.

So, the total work is:

W=3200π(782264.5)=3200π×517.5.W = 3200\pi \left( 782 - 264.5 \right) = 3200\pi \times 517.5.

Finally, we calculate:

W3200×3.1416×517.55,225,964.2 foot-pounds.W \approx 3200 \times 3.1416 \times 517.5 \approx 5,225,964.2 \text{ foot-pounds}.

Final Answer:

W5,225,964 foot-pounds.W \approx 5,225,964 \text{ foot-pounds}.


Would you like more details or have further questions on this? Here are some related questions to explore:

  1. How would the work change if the oil level were deeper?
  2. What is the role of the shape of the tank in determining the work required?
  3. How does the weight density of the oil affect the result?
  4. How can you calculate the total volume of oil in the tank?
  5. What other factors (like friction or temperature) could affect the work calculation?

Tip: When dealing with problems involving liquids or fluids, always remember that the work formula takes into account both the force (due to weight) and the distance (height to pump).

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Math Problem Analysis

Mathematical Concepts

Calculus
Fluid Mechanics
Integration

Formulas

W = ∫ F(y) dy
A = πr^2
dF = 50 × 64π dy
dW = (3200π dy) × (34 - y)
W = ∫_0^23 3200π (34 - y) dy

Theorems

Work-Energy Theorem
Integration of Force over Distance

Suitable Grade Level

College level (Calculus 1)