Math Problem Statement

A gas station stores its gasoline in a tank under the ground. The tank is a cylinder lying horizontally on its side. (In other words, the tank is not standing vertically on one of its flat ends.) If the radius of the cylinder is 2 meters, its length is 2 meters, and its top is 2 meters under the ground, find the total amount of work needed to pump the gasoline out of the tank. (The density of gasoline is 673 kilograms per cubic meter; use 𝑔=9.8 m/s2.)

Solution

To calculate the total amount of work required to pump the gasoline out of the cylindrical tank, we can use the following principles of work and fluid mechanics. The work required to pump the gasoline out is given by integrating the force needed to lift each differential volume of gasoline against gravity.

Step 1: Define Key Variables

  • The radius of the tank r=2r = 2 meters.
  • The length of the tank L=2L = 2 meters.
  • The density of gasoline ρ=673\rho = 673 kg/m³.
  • The acceleration due to gravity g=9.8g = 9.8 m/s².
  • The top of the tank is 2 meters under the ground, so we will assume that the gasoline needs to be pumped to a point 2 meters above the ground.

Step 2: General Idea of Work for Pumping

Work WW is given by the integral:

W=F(y)dyW = \int F(y) \, dy

where F(y)F(y) is the force required to lift the gasoline at height yy. The force is the weight of the differential volume of gasoline at height yy.

For a cylindrical tank lying horizontally, the height yy will vary from the bottom of the tank to the top of the tank, and we will need to compute the volume of gasoline at a given height yy inside the tank.

Step 3: Volume of Gasoline at Height yy

At a certain height yy inside the tank, the cross-section of the tank is a circle. The volume of the gasoline at height yy corresponds to a horizontal strip at that height, which has a certain width determined by the geometry of the circle.

The differential volume dVdV for a small strip at height yy is:

dV=A(y)LdydV = A(y) \cdot L \, dy

where A(y)A(y) is the area of the horizontal strip at height yy, and LL is the length of the cylinder (which is constant). The area A(y)A(y) can be found from geometry by determining the area of a circular segment.

Step 4: Force and Work Calculation

The weight of the gasoline in the strip is:

dW=ρgdVdW = \rho g dV

Thus, the total work is:

W=yminymaxρgA(y)L(hy)dyW = \int_{y_{\text{min}}}^{y_{\text{max}}} \rho g A(y) L \, (h - y) \, dy

where hh is the distance from the tank to the point above the ground where the gasoline is being pumped (in this case, h=4h = 4 meters, since the top of the tank is 2 meters underground and we're pumping 2 meters above the ground). yminy_{\text{min}} and ymaxy_{\text{max}} are the heights of the gasoline at the bottom and top of the tank, respectively.

This is the general setup for the work required. To compute it precisely, we would need to solve the integral by finding the exact area of the circular segment at each height yy.

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Math Problem Analysis

Mathematical Concepts

Work and Energy
Calculus
Fluid Mechanics
Geometry of Cylinders

Formulas

W = ∫ F(y) dy
dV = A(y) * L dy
dW = ρ * g * dV
W = ∫ ρ * g * A(y) * L * (h - y) dy

Theorems

Principle of Work
Volume of Cylindrical Segments

Suitable Grade Level

College Level - Physics/Engineering