Math Problem Statement

A tank has a shape of a cone with a radius at the top of 3 m and a height of 5 m. The tank also has a 1 m spout at the top of the tank. The tank is filled with water up to a height of 2 m. Find the work needed to pump all the water out the top of the spout. (Use 9.8 m/s2 for g and the fact that the density of water is 1000 kg/m3.)

Solution

We are tasked with finding the work required to pump water out of a conical tank with a spout. To solve this, we'll need to use the following concepts:

  • Density of water: ρ=1000kg/m3\rho = 1000 \, \text{kg/m}^3
  • Gravitational acceleration: g=9.8m/s2g = 9.8 \, \text{m/s}^2
  • The formula for work done in moving a volume of liquid against gravity is: W=FdyW = \int F \, dy where FF is the force, and dydy represents an infinitesimal change in height.

Step-by-step Plan:

  1. Volume Element: We'll first calculate the volume of an infinitesimal slice of water at a height yy above the bottom of the cone. Given the geometry of the cone, the radius of the water slice varies with height.

  2. Geometric Similarity: Since the tank is a cone, the radius rr at any height yy is proportional to the height from the tip of the cone. For this cone:

    • At the top y=5my = 5 \, \text{m}, the radius is 3m3 \, \text{m}.
    • Using the similarity of triangles: ry=35orr=35y\frac{r}{y} = \frac{3}{5} \quad \text{or} \quad r = \frac{3}{5} y
  3. Infinitesimal Volume dVdV: The infinitesimal volume dVdV of a slice of water at height yy with thickness dydy is the volume of a cylinder with radius r=35yr = \frac{3}{5} y and height dydy: dV=πr2dy=π(35y)2dy=π925y2dydV = \pi r^2 \, dy = \pi \left( \frac{3}{5} y \right)^2 \, dy = \pi \frac{9}{25} y^2 \, dy

  4. Force to Lift Water: The weight of this infinitesimal volume of water is ρgdV\rho g dV: dF=1000×9.8×π925y2dydF = 1000 \times 9.8 \times \pi \frac{9}{25} y^2 \, dy

  5. Distance to Lift Water: To pump water out of the spout, the water at height yy needs to be lifted a distance of 6y6 - y meters (since the spout is 1 meter above the top of the cone).

  6. Work for Infinitesimal Slice: The work to pump this infinitesimal slice is: dW=dF×(6y)=1000×9.8×π925y2(6y)dydW = dF \times (6 - y) = 1000 \times 9.8 \times \pi \frac{9}{25} y^2 \, (6 - y) \, dy

  7. Total Work: Integrate this expression from y=0y = 0 to y=2y = 2, as the tank is filled to a height of 2 meters: W=021000×9.8×π925y2(6y)dyW = \int_0^2 1000 \times 9.8 \times \pi \frac{9}{25} y^2 \, (6 - y) \, dy Simplifying constants: W=35280π02y2(6y)dyW = 35280 \pi \int_0^2 y^2 (6 - y) \, dy

Step-by-step Integration:

Now, we'll evaluate the integral: 02y2(6y)dy=026y2dy02y3dy\int_0^2 y^2 (6 - y) \, dy = \int_0^2 6y^2 \, dy - \int_0^2 y^3 \, dy

Let's calculate each part:

026y2dy=6[y33]02=6×83=16\int_0^2 6y^2 \, dy = 6 \left[ \frac{y^3}{3} \right]_0^2 = 6 \times \frac{8}{3} = 16 02y3dy=[y44]02=164=4\int_0^2 y^3 \, dy = \left[ \frac{y^4}{4} \right]_0^2 = \frac{16}{4} = 4 Thus, the total integral is: 164=1216 - 4 = 12

Final Work Calculation:

Now substitute this result into the expression for WW: W=35280π×12=423360πW = 35280 \pi \times 12 = 423360 \pi Approximating π3.1416\pi \approx 3.1416, we get: W423360×3.1416=1,329,305.6JW \approx 423360 \times 3.1416 = 1,329,305.6 \, \text{J}

Thus, the total work required to pump all the water out of the tank is approximately 1,329,305.6J\boxed{1,329,305.6} \, \text{J}.

Would you like more details or have any questions?

Here are 5 related questions for further exploration:

  1. How would the work change if the height of the spout were increased to 2 meters?
  2. What is the effect of changing the cone's base radius on the work required?
  3. How would the work differ if the tank were only half-filled with water?
  4. What if the water density were lower, like for oil (850 kg/m³)?
  5. How does the shape of the tank (e.g., cylindrical vs. conical) affect the work required?

Tip: Always check the dimensions of your parameters to ensure consistency when solving physics-related problems!

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Math Problem Analysis

Mathematical Concepts

Calculus
Volume of Revolution
Work-Energy Principle

Formulas

W = ∫ F dy
dV = π(3/5 y)^2 dy
dF = 1000 × 9.8 × dV
Work = ∫ 35280π y^2 (6 - y) dy

Theorems

Geometric Similarity
Work-Energy Theorem

Suitable Grade Level

Undergraduate Physics or Calculus Level