Math Problem Statement

Write a triple integral including limits of integration that gives the volume of the cap of the solid sphere x^2 + y^2 + z^2 ≤ 34 cut off by the plane z = 5 and restricted to the first octant. In your integral, use theta, rho, and phi for θ, ρ, and ϕ, as needed.

Solution

To set up the integral for the volume of the cap of the sphere in spherical coordinates, let's go through each part:

Step 1: Recognize Given Information

The equation of the sphere is x2+y2+z2=34x^2 + y^2 + z^2 = 34, which gives the radius ρ=34\rho = \sqrt{34} in spherical coordinates. The sphere is cut by the plane z=5z = 5, and we are only interested in the portion within the first octant.

Step 2: Choose Coordinate System

Since we're dealing with a sphere and have a cap defined by a plane, spherical coordinates are appropriate.

Step 3: Determine Limits for Spherical Coordinates

  1. For ρ\rho:

    • ρ\rho ranges from 0 to the radius of the sphere but is limited by the plane z=5z = 5.
    • In spherical coordinates, z=ρcosϕz = \rho \cos \phi.
    • Set ρcosϕ=5\rho \cos \phi = 5 to find the limit for ρ\rho, which gives ρ=5cosϕ\rho = \frac{5}{\cos \phi}.
    • Therefore, ρ\rho ranges from 00 to min(34,5cosϕ)\min(\sqrt{34}, \frac{5}{\cos \phi}).
  2. For θ\theta:

    • Since we are in the first octant, θ\theta (azimuthal angle) ranges from 00 to π2\frac{\pi}{2}.
  3. For ϕ\phi:

    • ϕ\phi (polar angle) is restricted to the portion above the plane z=5z = 5.
    • Given cosϕ=534\cos \phi = \frac{5}{\sqrt{34}}, ϕ\phi ranges from 00 to cos1(534)\cos^{-1} \left(\frac{5}{\sqrt{34}}\right).

Step 4: Integrate in Spherical Coordinates

The volume element in spherical coordinates is dV=ρ2sinϕdρdϕdθdV = \rho^2 \sin \phi \, d\rho \, d\phi \, d\theta.

Filling in the Blanks

  1. Coordinates used: spherical
  2. Limits of Integration:
    • a=0a = 0, b=π2b = \frac{\pi}{2} (for θ\theta)
    • c=0c = 0, d=cos1(534)d = \cos^{-1} \left(\frac{5}{\sqrt{34}}\right) (for ϕ\phi)
    • e=0e = 0, f=5cosϕf = \frac{5}{\cos \phi} (for ρ\rho)
  3. Integral Expression: Volume=0π20cos1(534)05cosϕρ2sinϕdρdϕdθ\text{Volume} = \int_0^{\frac{\pi}{2}} \int_0^{\cos^{-1} \left(\frac{5}{\sqrt{34}}\right)} \int_0^{\frac{5}{\cos \phi}} \rho^2 \sin \phi \, d\rho \, d\phi \, d\theta

Would you like further details on the integration process, or do you have questions about specific steps?


  1. How do spherical coordinates simplify triple integrals involving spheres?
  2. Why does the plane z=5z = 5 change the upper limit for ρ\rho?
  3. What role does the first octant restriction play in setting the limits?
  4. How would the limits change if it weren’t restricted to the first octant?
  5. What other coordinate systems could be used, and how would that affect the setup?

Tip: When setting up triple integrals in spherical coordinates, always focus on finding the radial, polar, and azimuthal limits separately based on geometric constraints.

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Math Problem Analysis

Mathematical Concepts

Triple Integrals
Spherical Coordinates
Volume of Solids

Formulas

Volume element in spherical coordinates dV = ρ^2 sin(φ) dρ dφ dθ

Theorems

Use of spherical coordinates for volume integration

Suitable Grade Level

Grades 11-12, College Level