- #1
alex.pasek
- 12
- 0
Homework Statement
Considering the vector Field F(x,y,z))(zx, zy, z2), and the domain whose boundary is provided by S=S1∪S2 with exterior orientation and
S1={(x,y,z)∈ℝ3 : z=6-2(x2+y2), 0≤z≤6},
S2={(x,y,z)∈ℝ3 : z=-6+2(x2+y2, -6≤z≤0}.
Compute the total flux of F across S.
Homework Equations
Gauss' Theorem.
The Attempt at a Solution
What I have thought to do was to compute ∫Fds across the surface S. For this I applied Gauss' Theorem to obtain that ∫Fds=∫∫∫(∇⋅F) dV
I would compute ∇⋅F= (∂/∂x, ∂/∂y, ∂/∂z) ⋅ (zx, zy, z2) = 4z
And now integrate it using a cylindrical change of variable.
x=rcos(θ)
y=rsin(θ)
z=z
With |J|=r
For D={0≤θ≤2π, -6≤z≤6, 0 ≤r≤√(z-6)/2} The limits for r are taken from the paraboloid equation.
For this I get a value of ∫Fds = ∫dθ∫dz∫√(z-6)/2r⋅4z⋅dr = 0 and the respective limits.
But a colleague states it is 144π as he computed it to be two paraboloids including the lower cover and multiplying that by 2.
Which result would be the correct one?
Thank you for your time.