Cylindrical shells (1 Viewer)

[ND]

When asked to show the volume of something using cylindrical shells (like when you're asked to show the integral, not just find the volume), are you allowed to use the 'consider the shell sliced and layed flat' type proof? If so, does anyone have a concise way of writing this? When i do it comes out being like a paragraph.

 

[freaking_out]

Originally posted by ND
When asked to show the volume of something using cylindrical shells (like when you're asked to show the integral, not just find the volume), are you allowed to use the 'consider the shell sliced and layed flat' type proof? If so, does anyone have a concise way of writing this? When i do it comes out being like a paragraph.

i dunno if i'm correct, but i usually just say the intergral of [2(pi)*(shell height)(shell radius)]dx....and then i work it out from there.

 

[ezzy85]

i say "consider a shell with volume pi(R² - r²)" i then expand that out and do the integral.

 

[ND]

Yeh i write that too..... when doing it by slices.

 

[freaking_out]

Originally posted by ND
Yeh i write that too..... when doing it by slices.

yeah...goodone.

 

[Newbie]

just draw it out you lazy bums

 

[freaking_out]

Originally posted by Newbie
just draw it out you lazy bums

but time is of the essence, in any 4u exam.

 

[Affinity]

what he meant was.. erh..
get fitzpatrick and arnold and compare them

 

[tonberry_kun]

don't u just write out all that crappy limits and delta V crap then state the formula?

 

[Fosweb]

I'm sure this has been asked before, but do we need to write the sigma notation for sum of shells before we say that you integrate to get volume?

 

[Saul]

hey, whats pi(R2 - r2) got to do with shells?

 

[Fosweb]

Its slices: annulus... (not shell method)
Area of bigger circle -- area of little circle.

 

[freaking_out]

Originally posted by Fosweb
I'm sure this has been asked before, but do we need to write the sigma notation for sum of shells before we say that you integrate to get volume?

my teacher said u gotta write it everytime.

 

[Affinity]

Originally posted by Saul
hey, whats pi(R2 - r2) got to do with shells?

that's for shells too.. if you are using the strict method.

the shell is really a annular cylinder

 

[Saul]

wouldn't it then be pi(R^2-r^2)*h?

 

[ricenoodles]

Originally posted by freaking_out
my teacher said u gotta write it everytime.

are u sure? because i always start my working with dV = pi(R+r)(R-r) etc

 

[freaking_out]

Originally posted by Saul
wouldn't it then be pi(R^2-r^2)*h?

yeah, well thats what he mean...

 

[ezzy85]

Originally posted by ricenoodles
are u sure? because i always start my working with dV = pi(R+r)(R-r) etc

thats the same as pi(R^2-r^2) and yeah, i forgot the *h

 

[Rahul]

Originally posted by ricenoodles
are u sure? because i always start my working with dV = pi(R+r)(R-r) etc

yes you have to. i remmeber my teacher mentioninf that you have to show its a sum of something or other...but the main thing, work from the start.

 

[Affinity]

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