Math Problem Statement

Evaluate the integral \( \iiint_D e^{(x^2 + y^2 + z^2)^{3/2}} \, dV \) where \( D \) is the region above the cone \( z = \sqrt{x^2 + y^2} \) and below the hemisphere \( z = \sqrt{1 - x^2 - y^2} \) using spherical coordinates.

Solution

To evaluate the given integral, we need to approach the problem using spherical coordinates due to the symmetry and the nature of the region DD.

Problem Setup

The integral is: De(x2+y2+z2)3/2dV\iiint_D e^{(x^2 + y^2 + z^2)^{3/2}} \, dV where DD is the region:

  1. Above the cone z=x2+y2z = \sqrt{x^2 + y^2},
  2. Below the hemisphere z=1x2y2z = \sqrt{1 - x^2 - y^2}.

Step 1: Transform to Spherical Coordinates

In spherical coordinates:

  • x=ρsinθcosϕx = \rho \sin\theta \cos\phi
  • y=ρsinθsinϕy = \rho \sin\theta \sin\phi
  • z=ρcosθz = \rho \cos\theta
  • The volume element dV=ρ2sinθdρdθdϕdV = \rho^2 \sin\theta \, d\rho \, d\theta \, d\phi.

Additionally, we have r2=x2+y2+z2=ρ2r^2 = x^2 + y^2 + z^2 = \rho^2, so (x2+y2+z2)3/2=ρ3(x^2 + y^2 + z^2)^{3/2} = \rho^3.

Step 2: Define the Limits

The region DD is bounded by:

  • The cone z=x2+y2z = \sqrt{x^2 + y^2}, which in spherical coordinates corresponds to θ=π4\theta = \frac{\pi}{4}.
  • The hemisphere z=1x2y2z = \sqrt{1 - x^2 - y^2}, which means ρ1\rho \leq 1.

Thus, the limits for integration are:

  • ρ\rho: from 0 to 1 (bounded by the hemisphere),
  • θ\theta: from 0 to π4\frac{\pi}{4} (bounded by the cone),
  • ϕ\phi: from 0 to 2π2\pi (full rotation around the z-axis).

Step 3: Set Up the Integral

Substituting these bounds and the expression for (x2+y2+z2)3/2=ρ3(x^2 + y^2 + z^2)^{3/2} = \rho^3, the integral becomes: 02π0π/401eρ3ρ2sinθdρdθdϕ\int_0^{2\pi} \int_0^{\pi/4} \int_0^1 e^{\rho^3} \cdot \rho^2 \sin\theta \, d\rho \, d\theta \, d\phi

Step 4: Solve the Integral

Separate the variables: 02πdϕ0π/4sinθdθ01ρ2eρ3dρ\int_0^{2\pi} d\phi \int_0^{\pi/4} \sin\theta \, d\theta \int_0^1 \rho^2 e^{\rho^3} \, d\rho

1. Integral over ϕ\phi:

02πdϕ=2π\int_0^{2\pi} d\phi = 2\pi

2. Integral over θ\theta:

0π/4sinθdθ=[cosθ]0π/4=122\int_0^{\pi/4} \sin\theta \, d\theta = \left[-\cos\theta\right]_0^{\pi/4} = 1 - \frac{\sqrt{2}}{2}

3. Integral over ρ\rho:

Let u=ρ3du=3ρ2dρdρ=du3ρ2u = \rho^3 \Rightarrow du = 3\rho^2 d\rho \Rightarrow d\rho = \frac{du}{3\rho^2}, giving: 01ρ2eρ3dρ=1301eudu=13(e1e0)=13(e1)\int_0^1 \rho^2 e^{\rho^3} \, d\rho = \frac{1}{3} \int_0^1 e^u \, du = \frac{1}{3} \left( e^1 - e^0 \right) = \frac{1}{3}(e - 1)

Step 5: Combine Results

Now, putting it all together: 2π(122)e13=2π3(122)(e1)2\pi \cdot \left(1 - \frac{\sqrt{2}}{2}\right) \cdot \frac{e - 1}{3} = \frac{2\pi}{3} \left(1 - \frac{\sqrt{2}}{2}\right)(e - 1)

This matches option B: 2π3(22)(e1)\boxed{\frac{2\pi}{3} (2 - \sqrt{2})(e - 1)}

Would you like further details on any of these steps or have any other questions?

Additional Questions

  1. How does the cone's equation affect the integration limits in spherical coordinates?
  2. Why is spherical coordinates preferred over Cartesian for this integral?
  3. What is the significance of eρ3e^{\rho^3} in the integrand?
  4. Can we generalize this approach for other cone-hemisphere intersections?
  5. What is the physical interpretation of this integral in a real-world scenario?

Tip

In spherical coordinates, always verify the bounds by examining each surface’s shape relative to spherical angles to avoid incorrect integration limits.

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Math Problem Analysis

Mathematical Concepts

Spherical Coordinates
Triple Integrals
Volume Integration

Formulas

Spherical coordinates: \( x = \rho \sin\theta \cos\phi \), \( y = \rho \sin\theta \sin\phi \), \( z = \rho \cos\theta \)
Volume element in spherical coordinates: \( dV = \rho^2 \sin\theta \, d\rho \, d\theta \, d\phi \)

Theorems

Integration in Spherical Coordinates

Suitable Grade Level

University Level (Calculus III or Multivariable Calculus)