Pappus' Theorem (surface area)

[whatlifeforme]

Homework Statement

Use Pappus' Theorem for surface area and the fact that the surface area of a sphere of radius c is 4(pi)c^2 to find the centroid of the semicircle x= sqrt ( c^2 - y^2)

Homework Equations

S = 2 (pi) * p * L

where s=surface area; p=distance from axis of revolution; L= length of the arc

The Attempt at a Solution

1. centroid of semicircle. should i put the equation in circle form, and attempt to solve from that?

 

[Dick]

Homework Statement

Use Pappus' Theorem for surface area and the fact that the surface area of a sphere of radius c is 4(pi)c^2 to find the centroid of the semicircle x= sqrt ( c^2 - y^2)

Homework Equations

S = 2 (pi) * p * L

where s=surface area; p=distance from axis of revolution; L= length of the arc

The Attempt at a Solution

1. centroid of semicircle. should i put the equation in circle form, and attempt to solve from that?

No, you don't. You need to think about what that equation means and how it's related to what you want to find. It's almost all you need to know.

 

[whatlifeforme]

i'm still lost.

 

[Dick]

i'm still lost.

Explain to me what the variables in that equation mean. Yes, S=surface area. But surface area of WHAT? Look it up if you don't have a good reference handy.

 

[whatlifeforme]

S = 2 (pi) * p * L

where s=surface area; p=distance from axis of revolution; L= length of the arc

 

[Dick]

S = 2 (pi) * p * L

where s=surface area; p=distance from axis of revolution; L= length of the arc

No progress, then? http://en.wikipedia.org/wiki/Pappus's_centroid_theorem