Find the volume between the cone $y = sqrt {x^2 + z^2} $ and the sphere $x^2 + y^2 + z^2 = 49$.
$begingroup$
Find the volume between the cone $y = sqrt {x^2 + z^2} $ and the sphere $x^2 + y^2 + z^2 = 49$.
I know that the volume we're interested in is the volume of the intersection between the sphere of radius $7$ and a an upside down cone in the direction of the $y$-axis, but I have no clue on how to set up the bounds of integration. I'm guessing we are supposed to do this in spherical coordinates, but how would we determine the limits of integration?
Thank you.
multivariable-calculus spherical-coordinates
$endgroup$
add a comment |
$begingroup$
Find the volume between the cone $y = sqrt {x^2 + z^2} $ and the sphere $x^2 + y^2 + z^2 = 49$.
I know that the volume we're interested in is the volume of the intersection between the sphere of radius $7$ and a an upside down cone in the direction of the $y$-axis, but I have no clue on how to set up the bounds of integration. I'm guessing we are supposed to do this in spherical coordinates, but how would we determine the limits of integration?
Thank you.
multivariable-calculus spherical-coordinates
$endgroup$
$begingroup$
same as if the cone were along the $z$ axis, so that using spherical coordinates it translates into a limit on just the polar angle. Thus switch $y$ and $z$ in the cone equation.
$endgroup$
– G Cab
Apr 9 '17 at 22:48
add a comment |
$begingroup$
Find the volume between the cone $y = sqrt {x^2 + z^2} $ and the sphere $x^2 + y^2 + z^2 = 49$.
I know that the volume we're interested in is the volume of the intersection between the sphere of radius $7$ and a an upside down cone in the direction of the $y$-axis, but I have no clue on how to set up the bounds of integration. I'm guessing we are supposed to do this in spherical coordinates, but how would we determine the limits of integration?
Thank you.
multivariable-calculus spherical-coordinates
$endgroup$
Find the volume between the cone $y = sqrt {x^2 + z^2} $ and the sphere $x^2 + y^2 + z^2 = 49$.
I know that the volume we're interested in is the volume of the intersection between the sphere of radius $7$ and a an upside down cone in the direction of the $y$-axis, but I have no clue on how to set up the bounds of integration. I'm guessing we are supposed to do this in spherical coordinates, but how would we determine the limits of integration?
Thank you.
multivariable-calculus spherical-coordinates
multivariable-calculus spherical-coordinates
edited Apr 10 '17 at 16:27
Nosrati
26.5k62354
26.5k62354
asked Apr 9 '17 at 22:28
JC1JC1
7127
7127
$begingroup$
same as if the cone were along the $z$ axis, so that using spherical coordinates it translates into a limit on just the polar angle. Thus switch $y$ and $z$ in the cone equation.
$endgroup$
– G Cab
Apr 9 '17 at 22:48
add a comment |
$begingroup$
same as if the cone were along the $z$ axis, so that using spherical coordinates it translates into a limit on just the polar angle. Thus switch $y$ and $z$ in the cone equation.
$endgroup$
– G Cab
Apr 9 '17 at 22:48
$begingroup$
same as if the cone were along the $z$ axis, so that using spherical coordinates it translates into a limit on just the polar angle. Thus switch $y$ and $z$ in the cone equation.
$endgroup$
– G Cab
Apr 9 '17 at 22:48
$begingroup$
same as if the cone were along the $z$ axis, so that using spherical coordinates it translates into a limit on just the polar angle. Thus switch $y$ and $z$ in the cone equation.
$endgroup$
– G Cab
Apr 9 '17 at 22:48
add a comment |
2 Answers
2
active
oldest
votes
$begingroup$
If you want to do it in spherical coordinates notice $z=sqrt{x^2+y^2}$ translates to $z=r$ and $x^2+y^2+z^2=49$ translates to $rho=7$.
If $z=r$ then $frac{r}{z}=tan (phi)=1$ so $y=r$ translates to $phi=frac{pi}{4}$.
Hence what we have is,
$$V=int_{0}^{2pi} int_{0}^{frac{pi}{4}} int_{0}^{7} rho^2 sin (phi) drho dphi dtheta$$
Actually because we have $y=sqrt{x^2+z^2}$ I would define a modified version of spherical coordinates. Let $x^2+z^2=r^2$, let $phi$ be angle with positive $y$ axis of a point to the origin with the restriction that $0 leq phi leq pi$. Let $rho$ be the distance from the origin. Let $theta$ be the counterclockwise angle in the $(x,z)$ plane with the positive $x$ axis.
Then I would compute the Jacobian and it will turn out to be $rho^2 sin (phi)$. The equation $frac{r}{y}=tan (phi)$ will hold and calculations will be pretty much identical.
Think about why $frac{r}{z}=tan (phi)$. Image from Paul's math.
$endgroup$
$begingroup$
Hi, I've previously entered the wrong equation - its now corrected. Apologies
$endgroup$
– JC1
Apr 9 '17 at 22:40
$begingroup$
Ah, thank you - did not think about that. Also, how did you tell that $r/z = tan(phi)$
$endgroup$
– JC1
Apr 9 '17 at 22:45
$begingroup$
I've added a picture.
$endgroup$
– Ahmed S. Attaalla
Apr 9 '17 at 22:51
$begingroup$
Oh ok. Since $ z = r$, we can say that the angle between of $phi$ will need to be $tan(phi) = z/r $ using SOHCAHTOA . Thank you
$endgroup$
– JC1
Apr 9 '17 at 22:55
$begingroup$
You mean $frac{r}{z}$ right.
$endgroup$
– Ahmed S. Attaalla
Apr 9 '17 at 22:57
|
show 3 more comments
$begingroup$
For given input eliminate $x,z$ etc. and you are left with a circle on the sphere:
$$ x= 7/sqrt2 ,y= 7/sqrt2 ,cos t, z= 7/sqrt2 , sin t $$
You can use established result Gauss Bonnet thm to advantage, since $k_g , K $ are constant as a differential geometry approach.
$$ k_g= frac{1}{7},, s= 2 pi frac{7}{sqrt2},, int k_g ds = frac{pi}{sqrt2} $$
Integral curvature (solid angle)
$$ int int K dA = 2 pi- frac{ pi}{sqrt2}$$
and Volume is solid angle times $R^3/3$
$$= pi(2 - frac{ 1}{sqrt2}) , frac{7^3}{3}. $$
$endgroup$
add a comment |
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2 Answers
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2 Answers
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$begingroup$
If you want to do it in spherical coordinates notice $z=sqrt{x^2+y^2}$ translates to $z=r$ and $x^2+y^2+z^2=49$ translates to $rho=7$.
If $z=r$ then $frac{r}{z}=tan (phi)=1$ so $y=r$ translates to $phi=frac{pi}{4}$.
Hence what we have is,
$$V=int_{0}^{2pi} int_{0}^{frac{pi}{4}} int_{0}^{7} rho^2 sin (phi) drho dphi dtheta$$
Actually because we have $y=sqrt{x^2+z^2}$ I would define a modified version of spherical coordinates. Let $x^2+z^2=r^2$, let $phi$ be angle with positive $y$ axis of a point to the origin with the restriction that $0 leq phi leq pi$. Let $rho$ be the distance from the origin. Let $theta$ be the counterclockwise angle in the $(x,z)$ plane with the positive $x$ axis.
Then I would compute the Jacobian and it will turn out to be $rho^2 sin (phi)$. The equation $frac{r}{y}=tan (phi)$ will hold and calculations will be pretty much identical.
Think about why $frac{r}{z}=tan (phi)$. Image from Paul's math.
$endgroup$
$begingroup$
Hi, I've previously entered the wrong equation - its now corrected. Apologies
$endgroup$
– JC1
Apr 9 '17 at 22:40
$begingroup$
Ah, thank you - did not think about that. Also, how did you tell that $r/z = tan(phi)$
$endgroup$
– JC1
Apr 9 '17 at 22:45
$begingroup$
I've added a picture.
$endgroup$
– Ahmed S. Attaalla
Apr 9 '17 at 22:51
$begingroup$
Oh ok. Since $ z = r$, we can say that the angle between of $phi$ will need to be $tan(phi) = z/r $ using SOHCAHTOA . Thank you
$endgroup$
– JC1
Apr 9 '17 at 22:55
$begingroup$
You mean $frac{r}{z}$ right.
$endgroup$
– Ahmed S. Attaalla
Apr 9 '17 at 22:57
|
show 3 more comments
$begingroup$
If you want to do it in spherical coordinates notice $z=sqrt{x^2+y^2}$ translates to $z=r$ and $x^2+y^2+z^2=49$ translates to $rho=7$.
If $z=r$ then $frac{r}{z}=tan (phi)=1$ so $y=r$ translates to $phi=frac{pi}{4}$.
Hence what we have is,
$$V=int_{0}^{2pi} int_{0}^{frac{pi}{4}} int_{0}^{7} rho^2 sin (phi) drho dphi dtheta$$
Actually because we have $y=sqrt{x^2+z^2}$ I would define a modified version of spherical coordinates. Let $x^2+z^2=r^2$, let $phi$ be angle with positive $y$ axis of a point to the origin with the restriction that $0 leq phi leq pi$. Let $rho$ be the distance from the origin. Let $theta$ be the counterclockwise angle in the $(x,z)$ plane with the positive $x$ axis.
Then I would compute the Jacobian and it will turn out to be $rho^2 sin (phi)$. The equation $frac{r}{y}=tan (phi)$ will hold and calculations will be pretty much identical.
Think about why $frac{r}{z}=tan (phi)$. Image from Paul's math.
$endgroup$
$begingroup$
Hi, I've previously entered the wrong equation - its now corrected. Apologies
$endgroup$
– JC1
Apr 9 '17 at 22:40
$begingroup$
Ah, thank you - did not think about that. Also, how did you tell that $r/z = tan(phi)$
$endgroup$
– JC1
Apr 9 '17 at 22:45
$begingroup$
I've added a picture.
$endgroup$
– Ahmed S. Attaalla
Apr 9 '17 at 22:51
$begingroup$
Oh ok. Since $ z = r$, we can say that the angle between of $phi$ will need to be $tan(phi) = z/r $ using SOHCAHTOA . Thank you
$endgroup$
– JC1
Apr 9 '17 at 22:55
$begingroup$
You mean $frac{r}{z}$ right.
$endgroup$
– Ahmed S. Attaalla
Apr 9 '17 at 22:57
|
show 3 more comments
$begingroup$
If you want to do it in spherical coordinates notice $z=sqrt{x^2+y^2}$ translates to $z=r$ and $x^2+y^2+z^2=49$ translates to $rho=7$.
If $z=r$ then $frac{r}{z}=tan (phi)=1$ so $y=r$ translates to $phi=frac{pi}{4}$.
Hence what we have is,
$$V=int_{0}^{2pi} int_{0}^{frac{pi}{4}} int_{0}^{7} rho^2 sin (phi) drho dphi dtheta$$
Actually because we have $y=sqrt{x^2+z^2}$ I would define a modified version of spherical coordinates. Let $x^2+z^2=r^2$, let $phi$ be angle with positive $y$ axis of a point to the origin with the restriction that $0 leq phi leq pi$. Let $rho$ be the distance from the origin. Let $theta$ be the counterclockwise angle in the $(x,z)$ plane with the positive $x$ axis.
Then I would compute the Jacobian and it will turn out to be $rho^2 sin (phi)$. The equation $frac{r}{y}=tan (phi)$ will hold and calculations will be pretty much identical.
Think about why $frac{r}{z}=tan (phi)$. Image from Paul's math.
$endgroup$
If you want to do it in spherical coordinates notice $z=sqrt{x^2+y^2}$ translates to $z=r$ and $x^2+y^2+z^2=49$ translates to $rho=7$.
If $z=r$ then $frac{r}{z}=tan (phi)=1$ so $y=r$ translates to $phi=frac{pi}{4}$.
Hence what we have is,
$$V=int_{0}^{2pi} int_{0}^{frac{pi}{4}} int_{0}^{7} rho^2 sin (phi) drho dphi dtheta$$
Actually because we have $y=sqrt{x^2+z^2}$ I would define a modified version of spherical coordinates. Let $x^2+z^2=r^2$, let $phi$ be angle with positive $y$ axis of a point to the origin with the restriction that $0 leq phi leq pi$. Let $rho$ be the distance from the origin. Let $theta$ be the counterclockwise angle in the $(x,z)$ plane with the positive $x$ axis.
Then I would compute the Jacobian and it will turn out to be $rho^2 sin (phi)$. The equation $frac{r}{y}=tan (phi)$ will hold and calculations will be pretty much identical.
Think about why $frac{r}{z}=tan (phi)$. Image from Paul's math.
edited Apr 9 '17 at 23:24
answered Apr 9 '17 at 22:36
Ahmed S. AttaallaAhmed S. Attaalla
14.8k12050
14.8k12050
$begingroup$
Hi, I've previously entered the wrong equation - its now corrected. Apologies
$endgroup$
– JC1
Apr 9 '17 at 22:40
$begingroup$
Ah, thank you - did not think about that. Also, how did you tell that $r/z = tan(phi)$
$endgroup$
– JC1
Apr 9 '17 at 22:45
$begingroup$
I've added a picture.
$endgroup$
– Ahmed S. Attaalla
Apr 9 '17 at 22:51
$begingroup$
Oh ok. Since $ z = r$, we can say that the angle between of $phi$ will need to be $tan(phi) = z/r $ using SOHCAHTOA . Thank you
$endgroup$
– JC1
Apr 9 '17 at 22:55
$begingroup$
You mean $frac{r}{z}$ right.
$endgroup$
– Ahmed S. Attaalla
Apr 9 '17 at 22:57
|
show 3 more comments
$begingroup$
Hi, I've previously entered the wrong equation - its now corrected. Apologies
$endgroup$
– JC1
Apr 9 '17 at 22:40
$begingroup$
Ah, thank you - did not think about that. Also, how did you tell that $r/z = tan(phi)$
$endgroup$
– JC1
Apr 9 '17 at 22:45
$begingroup$
I've added a picture.
$endgroup$
– Ahmed S. Attaalla
Apr 9 '17 at 22:51
$begingroup$
Oh ok. Since $ z = r$, we can say that the angle between of $phi$ will need to be $tan(phi) = z/r $ using SOHCAHTOA . Thank you
$endgroup$
– JC1
Apr 9 '17 at 22:55
$begingroup$
You mean $frac{r}{z}$ right.
$endgroup$
– Ahmed S. Attaalla
Apr 9 '17 at 22:57
$begingroup$
Hi, I've previously entered the wrong equation - its now corrected. Apologies
$endgroup$
– JC1
Apr 9 '17 at 22:40
$begingroup$
Hi, I've previously entered the wrong equation - its now corrected. Apologies
$endgroup$
– JC1
Apr 9 '17 at 22:40
$begingroup$
Ah, thank you - did not think about that. Also, how did you tell that $r/z = tan(phi)$
$endgroup$
– JC1
Apr 9 '17 at 22:45
$begingroup$
Ah, thank you - did not think about that. Also, how did you tell that $r/z = tan(phi)$
$endgroup$
– JC1
Apr 9 '17 at 22:45
$begingroup$
I've added a picture.
$endgroup$
– Ahmed S. Attaalla
Apr 9 '17 at 22:51
$begingroup$
I've added a picture.
$endgroup$
– Ahmed S. Attaalla
Apr 9 '17 at 22:51
$begingroup$
Oh ok. Since $ z = r$, we can say that the angle between of $phi$ will need to be $tan(phi) = z/r $ using SOHCAHTOA . Thank you
$endgroup$
– JC1
Apr 9 '17 at 22:55
$begingroup$
Oh ok. Since $ z = r$, we can say that the angle between of $phi$ will need to be $tan(phi) = z/r $ using SOHCAHTOA . Thank you
$endgroup$
– JC1
Apr 9 '17 at 22:55
$begingroup$
You mean $frac{r}{z}$ right.
$endgroup$
– Ahmed S. Attaalla
Apr 9 '17 at 22:57
$begingroup$
You mean $frac{r}{z}$ right.
$endgroup$
– Ahmed S. Attaalla
Apr 9 '17 at 22:57
|
show 3 more comments
$begingroup$
For given input eliminate $x,z$ etc. and you are left with a circle on the sphere:
$$ x= 7/sqrt2 ,y= 7/sqrt2 ,cos t, z= 7/sqrt2 , sin t $$
You can use established result Gauss Bonnet thm to advantage, since $k_g , K $ are constant as a differential geometry approach.
$$ k_g= frac{1}{7},, s= 2 pi frac{7}{sqrt2},, int k_g ds = frac{pi}{sqrt2} $$
Integral curvature (solid angle)
$$ int int K dA = 2 pi- frac{ pi}{sqrt2}$$
and Volume is solid angle times $R^3/3$
$$= pi(2 - frac{ 1}{sqrt2}) , frac{7^3}{3}. $$
$endgroup$
add a comment |
$begingroup$
For given input eliminate $x,z$ etc. and you are left with a circle on the sphere:
$$ x= 7/sqrt2 ,y= 7/sqrt2 ,cos t, z= 7/sqrt2 , sin t $$
You can use established result Gauss Bonnet thm to advantage, since $k_g , K $ are constant as a differential geometry approach.
$$ k_g= frac{1}{7},, s= 2 pi frac{7}{sqrt2},, int k_g ds = frac{pi}{sqrt2} $$
Integral curvature (solid angle)
$$ int int K dA = 2 pi- frac{ pi}{sqrt2}$$
and Volume is solid angle times $R^3/3$
$$= pi(2 - frac{ 1}{sqrt2}) , frac{7^3}{3}. $$
$endgroup$
add a comment |
$begingroup$
For given input eliminate $x,z$ etc. and you are left with a circle on the sphere:
$$ x= 7/sqrt2 ,y= 7/sqrt2 ,cos t, z= 7/sqrt2 , sin t $$
You can use established result Gauss Bonnet thm to advantage, since $k_g , K $ are constant as a differential geometry approach.
$$ k_g= frac{1}{7},, s= 2 pi frac{7}{sqrt2},, int k_g ds = frac{pi}{sqrt2} $$
Integral curvature (solid angle)
$$ int int K dA = 2 pi- frac{ pi}{sqrt2}$$
and Volume is solid angle times $R^3/3$
$$= pi(2 - frac{ 1}{sqrt2}) , frac{7^3}{3}. $$
$endgroup$
For given input eliminate $x,z$ etc. and you are left with a circle on the sphere:
$$ x= 7/sqrt2 ,y= 7/sqrt2 ,cos t, z= 7/sqrt2 , sin t $$
You can use established result Gauss Bonnet thm to advantage, since $k_g , K $ are constant as a differential geometry approach.
$$ k_g= frac{1}{7},, s= 2 pi frac{7}{sqrt2},, int k_g ds = frac{pi}{sqrt2} $$
Integral curvature (solid angle)
$$ int int K dA = 2 pi- frac{ pi}{sqrt2}$$
and Volume is solid angle times $R^3/3$
$$= pi(2 - frac{ 1}{sqrt2}) , frac{7^3}{3}. $$
edited Apr 10 '17 at 13:19
answered Apr 9 '17 at 23:16
NarasimhamNarasimham
20.8k52158
20.8k52158
add a comment |
add a comment |
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$begingroup$
same as if the cone were along the $z$ axis, so that using spherical coordinates it translates into a limit on just the polar angle. Thus switch $y$ and $z$ in the cone equation.
$endgroup$
– G Cab
Apr 9 '17 at 22:48