- #1
MrMaterial
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Homework Statement
This is a book problem, as follows: Find the volume between the cone x = [itex]\sqrt{y^{2}+x^{2}}[/itex] and the sphere x[itex]^{2}[/itex]+y[itex]^{2}[/itex]+z[itex]^{2}[/itex] = 4
Homework Equations
spherical coordinates:
p[itex]^{2}[/itex]=x[itex]^{2}[/itex]+y[itex]^{2}[/itex]+z[itex]^{2}[/itex]
[itex]\phi[/itex] = angle from Z axis (as I understand it)
[itex]\theta[/itex] = angle from x or y axis
The Attempt at a Solution
I am confused on what solid they are referring to, so I will do it in two different ways.
I will first solve it assuming it is the volume of the cone (cone with spherical top)
It seems obvious that this is best solved using spherical coordinates.
First looking at the cone, it is a cone that appears on its side as it travels in the direction of the x axis.
Looking at the sphere, it is simply a sphere centered at the origin with a radius of [itex]\sqrt{4}[/itex]
At this point I start setting up the triple integral.
[itex]\int\int\int[/itex]p[itex]^{2}[/itex]sin([itex]\phi[/itex])dpd[itex]\phi[/itex]d[itex]\theta[/itex]
p is going to go from 0 to [itex]\sqrt{4}[/itex]
[itex]\phi[/itex] is going to go from [itex]\pi[/itex]/4 to 3[itex]\pi[/itex]/4
θ is going from -[itex]\pi[/itex]/4 to [itex]\pi[/itex]/4
Then i punch it into the calculator and I get 4[itex]\pi[/itex]([itex]\sqrt{2}[/itex]/3)
The book answer is 16[itex]\pi[/itex](([itex]\sqrt{2}[/itex]-1)/(3[itex]\sqrt{2}[/itex]))
For my second answer I will assume they want me to find the volume of the sphere, then subtract my former answer (the cone with spherical top)
First I will find the volume of the sphere
p is going to go from 0 to [itex]\sqrt{4}[/itex]
[itex]\phi[/itex] is going to go from 0 to [itex]\pi[/itex]
θ is going from 0 to 2[itex]\pi[/itex]
punch it into the ol' calculator and I get 32[itex]\pi[/itex]/3
then I subtract my previous answer and I get
27.59
The book answer to this problem in decimal form is 9.815
So I must have found the volume of the wrong solid, or i set up my integrals wrong? Can any of you tell by looking at my work?
thanks!