JASON or RITA...HELP!!! (or anyone else)

[jencowman]

I have to a math problem I am stuck with and I have to turn my hw in tomorrow at 9am...so any help would be MUCH appreciated

Comments

[wcu]

wouldnt it just be the integral of the area given the distance?

80cm/sec * 4sec = 320cm = radius of the circle.

area of circle = pi r ^2 = pi * 320^2, so the integral from 0 to 320 of pi r^2?

i think.. i havent done these things in a while and im kind of just coming up with shit off the top of my head

[jencowman]

if i wanted to do it implicitly, how would i set it up...? I know i need to find da/dt, and I know that A=pi*r^2, and i need to replace r by an expression involving t...so... dist = rate*time...so r=80t..so pi(80t)^2...but I have no clue how to set it up because i havent had any math since my senior yr of HS!

[wcu]

yes yes... but you say you want the derivative? i say integral.. maybe im wrong though?

i believe it would just be the integral of your equation using t as the variable that is changing:

Integral from 0 to 4 of pi(80t)^2 --- right?

this can be written as pi*80*80 * integral from 0 to 4 of t^2

this is 20096 * [1/3 * t^3]|from 0 to 4 = 20096 * 21.333333 = 428714.66cm/sec

right? that sounds way big though.. but i think my reasoning is on the right track. dont blame me for your failures! ;)

[jencowman]

we havent done integrals yet...so i'm thinking derivative...i dont know anymore

[sidekickrita]

EXCITING. still need it?

[jencowman]

YES

[sidekickrita]

so dr/dt=80 cm/s, and we need da/dt at 4 s.

a=pi*r^2

da/dt=2*pi*r*dr/dt

da/dt=(2)(pi)(80cm/s*4s)(80cm/s)

i think?

[jencowman]

heartheartheart