View Full Version : Stupid Math ...

ss3079

10-29-2003, 07:21 PM

Got a cylinder with no top.

250 square cm's of fiberglass.

r cm's would represent the base radius of this cylinder. What is the cubic function? What are the dimensions of the cylinder when it has 200mL in it? Not only what is it, how did you get it ... this could really come in handy later on for me.

I was thinking along the lines of V=pir^2h ... C=2r ... = 2pir+pir^2 ... whaaaaat the ... :wow:

What this has to do with boxes ... you shall see.

Much appreciated.

- Steve

ss3079

10-29-2003, 07:26 PM

And if you don't know the height, or any dimensions ... where I'm confused.

- Steve

ss3079

10-29-2003, 07:50 PM

I need to know the cubic function of a cylinder with no top made out of 250 cm^2 of fiberglass, or metal, whatever. First of all.

- Steve :confused:

jbl_marshall21

10-29-2003, 07:52 PM

You don't know any dimensions, but you need a cylinder to handle 200 mL ?

so screwed. steve if u get boggled up, i took geometry last year (passed wit a 91) but i'm sure u know what ur doing. :veryhappy

ss3079

10-29-2003, 08:03 PM

so screwed. steve if u get boggled up, i took geometry last year (passed wit a 91) but i'm sure u know what ur doing. :veryhappy

So this guy makes a can with 250cm^2 of metal, fiberglass, whatever ... with no top.

So you let r cm's represent the base radius. What is the volume of the can as a cubic function of r ?

Im really confused.

- Steve

Wonderbread

10-29-2003, 08:07 PM

you want a function for the volume of the cylinder with a surface area of 250 cm^2... it's a **** good thing I understand Stevenglish...

ss3079

10-29-2003, 08:09 PM

you want a function for the volume of the cylinder with a surface area of 250 cm^2... it's a **** good thing I understand Stevenglish...

Yeah well thats as good as it gets ;)

- Steve

Wonderbread

10-29-2003, 08:29 PM

not sure if this is right...

you never know, lol.

V = (Pi*r^2)[(250-Pi*r^2)/p]

Pi = Pi...

r= radius

p = perimeter

jbl_marshall21

10-29-2003, 08:35 PM

So this guy makes a can with 250cm^2 of metal, fiberglass, whatever ... with no top.

So you let r cm's represent the base radius. What is the volume of the can as a cubic function of r ?

Im really confused.

- Steve

SA=250cm^2

thats without a top. hmmm tricky :furious: let me think here. aah yes nah nevermind i can't remember the the surface area formula of a cylinder.

its right on the tip of tounge. ****'t if u don't figure it out tonight i'll get it tomorrow. i'll see if my math teacher can get it cuz i don't remember the **** formula. wait is it circumference X height + the area on the bottom?

ss3079

10-29-2003, 08:35 PM

Thanks much ... we'll see if it works.

- Steve :moon:

jbl_marshall21

10-29-2003, 08:37 PM

not sure if this is right...

you never know, lol.

V = (Pi*r^2)[(250-Pi*r^2)/p]

Pi = Pi...

r= radius

p = perimeter

perimeter on a cylinder???????? :banghead:

ss3079

10-29-2003, 08:42 PM

Who knows, I'm pretty confused right now ...

A can with no top is made from 250cm^2 of fiberglass. 'r' cm's would rep. the base radius of the can. Need the volume of the can as a cubic function of 'r'.

I've gotten things scribbled down here ...

SA= 250cm^3 = Pi*r^2 + 2Pi*r*h

V= h*Pi*r^2

V= (Pi*r^2)[(250-Pi*r^2)/p)

V= 250r - Pi*r^3 / 2

Last one catches my eye. But why, and how ...

- Steve

Wonderbread

10-29-2003, 09:45 PM

http://www.math.com/school/subject3/images/S3U4L4DP1.gif

http://www.math.com/school/subject3/images/S3U4L4DP2.gif

http://www.math.com/school/subject3/images/S3U4L4DP3.gif

Surface Area of a Cylinder = 2 pi r^2 + s r h

Surface Area = Areas of top and bottom +Area of the side

Surface Area = 2(Area of top) + (perimeter of top)* height

Surface Area = 2(pi r^2) + (2 pi r)* h

250 = (pi*r^2) + [(2pi*r)*h]

Isolate for ‘h’

h = [(250-pi*r^2)/(2pi*r)]

V=Pi*r*h

V = pi*r * [(250-pi*r^2)/(2pi*r)]

There… ass….

awalbert88

10-29-2003, 10:18 PM

Uhm...

I'm going to go grab a soda and then come back to this one. I think I need some caffeine if I'm going to understand this.

Wonderbread

10-29-2003, 10:52 PM

I took off the top in my calculations... hence me not multiplying by 2... ***.. :p there is a bottom to the cylinder.

jbl_marshall21

10-30-2003, 09:12 AM

I took off the top in my calculations... hence me not multiplying by 2... ***.. :p there is a bottom to the cylinder.

good job...

ss3079

10-30-2003, 02:04 PM

Thanks much ...

You've done well for skipping so many classes, Jer ;)

- Steve

Wonderbread

10-30-2003, 02:53 PM

It says to express it as a function of r^3, *** ... Therefore I'm right, I win ...

r^3? that's ridiculous... why would anyone do that?? teh right way to do it is to multiply r^2 by r.... that's how it's done...***

Wonderbread

10-30-2003, 02:54 PM

Thanks much ...

You've done well for skipping so many classes, Jer ;)

- Steve

in my senoior year of high school, I had 3 classes a day second semester, I went to 1 every day... the same one... and sometimes I even went to calculus if I needed a nap or a break from playing frisbee... heck, sometimes I played frisbee in class... no word of a lie... we played for almost 20 minutes before he noticed...

awalbert88

10-30-2003, 04:09 PM

in my senoior year of high school, I had 3 classes a day second semester, I went to 1 every day... the same one... and sometimes I even went to calculus if I needed a nap or a break from playing frisbee... heck, sometimes I played frisbee in class... no word of a lie... we played for almost 20 minutes before he noticed...

****. I only ever got away with playing cards or napping in class. Never tried frisbee. I still kinda miss high school for that reason.. always somebody to play a good card game with.

ss3079

10-30-2003, 04:30 PM

in my senoior year of high school, I had 3 classes a day second semester, I went to 1 every day... the same one... and sometimes I even went to calculus if I needed a nap or a break from playing frisbee... heck, sometimes I played frisbee in class... no word of a lie... we played for almost 20 minutes before he noticed...

Lol ... I remember those days .... second semester's were always Wood, Wood, English, and PE or something of the like.

- Steve

Wonderbread

10-30-2003, 04:54 PM

oh, I had Chem 30 (Grade 12), Computer Programming 30, and Math 31 (pre-calculus)... I only went to Chem, it was the final mark I needed for university... pre-calc was the one that I palyed frisbee in... that was fun... That'll learn 'em real good for sending me m diploma in like february.