Comments on: Small Increments & Approximations – A Familiar-Looking Inverted Cone of Water

By: Miss Loi

Miss Loi — Mon, 22 Oct 2007 17:50:10 +0000

But of course! How many times have you seen 1/3 πr²h served to you on a platter?

By: stupid question

stupid question — Mon, 22 Oct 2007 16:52:35 +0000

ok a stupid question. must memorise figure formulas anot ar. like cone. ok probably too late to ask.

By: Miss Loi

Miss Loi — Sun, 30 Sep 2007 16:26:05 +0000

Now that it's O-Level crunch time, more familiar 'must-do' questions will be coming your way.

Do ask your fellow ~~sufferers~~ friends to come here to get an idea of the commonly recurring questions and also burn some joss sticks!

By: 123

123 — Sun, 30 Sep 2007 05:45:22 +0000

Familiar TYS qn....

By: Miss Loi

Miss Loi — Sat, 05 May 2007 14:31:30 +0000

Kiroii, answer correcto but working a little incorrecto which Miss Loi already corrected in red for you. Judging by the time of your answer, think you're a bit sleepy lah. Mossie see how the model student did it??? You can't just anyhow substitute the x values directly into the above volume formula! You are finding the change in V (i.e. dV) with respect to a small change in x (i.e. dx) so you die die have to differentiate first!

By: Kiroii

Kiroii — Fri, 04 May 2007 18:22:53 +0000

r = 3/5x
v= 1/3 π r^2 h
v= 1/3 π 9x^2/25 x
v= 3πx^3/ 25
v=3π/25)x3 (shown)

dv/dx = 9/3625π x^2 (thro quotion rule)
delta v = dv/dx times 0.2 (with x as 3)
delta v = 0.648 π
correcto?

By: Mossie`Ol Chin

Mossie`Ol Chin — Fri, 06 Apr 2007 00:27:04 +0000

hahaha... i can't imagine if my teacher ever jumps up and down, left and right like a siaw char boh...

By: Miss Loi

Miss Loi — Thu, 05 Apr 2007 15:47:42 +0000

Mossie you sure sound like an over-aged student!

Part 1 is correct as you rightly used similar triangles for the proving.

But Part 2 is WRONG! Wrong approach! Wrong formula! WRONG WRONG WRONG!!! *jumps up and down like a siow char bo*

So *tidies hair* I think your 6 years of rustiness is showing

Students, this question is still open - keep trying!

By: Mossie`Ol Chin

Mossie`Ol Chin — Thu, 05 Apr 2007 12:31:12 +0000

woah, that was challenging... been like almost 6 years since i last attempted such quesion.

let the unknown radius of the cone with x height be rx

by porportion,

rx = 6x/10

Therefore, by the cone formula

Vx = 1/3π(6x/10)^2*x
= (3π/25)x3

correct?

the 2nd part, Vx3.02-Vx3.00 or

3/25π[(x a)^3 - x^3)
= 3/25π[x^2a xa^2 a^3]

so, let x = 3 and a = 2, and u can solve for the differences.

correct?

hahaha... really been long since i ever did this man!!!