# I need math help

Discussion in 'General Chat' started by Marki, Apr 9, 2007.

1. #1
from my AP calculus class, just decided to tackle the over spring break hw and realized i never #\$%#ing learned this shit

1. Suppose that a cup of cocoa cooled from 90 degrees C to 60 degrees C after 10 minutes in a room whose temperature was 20 degrees. How much longer would it take the cocoa to cool to 35 degrees C?

2. A radioactive substance decays at a rate proportional to the amount present. If one gram of a radioactive substance reduces .25 gram in four hours, find how long it will be until .1 gram remains.

3. A pizza heated to a temperature of 350 degrees Fahrenheit, is taken out of an oven and placed in a 75 degree F room at time t=0 minutes. The temperature of the pizza is changing at a rate of -110e^.4t degrees Fahrenheit per minute. To the nearest degree, what is the temperature of the pizza at time t=5 minutes?

2. #2
Graphing calculator, plot regressions...

3. #3
1 and 3 are newtons law of cooling problems. 2 is a halflife problem and they are the easiest type of differential equation. Look those terms up, there should be two equations with the variables defined somewhere in your textbook.

4. #4
Ae=Ao*.5 t/t(1/2) for the half life equation.

5. #5
t1/2 is 2hours
Ae is .1 grams
Ao is 1 gram
t needs to be solved

manipulate the equation:
so t=((logAe/logAo)/log.5)*t1/2

6. #6
Man, thats horribly wrong.

first you solve this for r:

.25 = 1*e^(r*(4*3600))

Then you solve this for t

.1 = 1*e^(r*t)

7. #7
You're right. I looked up the wrong equation from my textbook.

8. #8
#\$%# you, ive raped people for far less than this. you think you can #\$%#ing come on SC.NET and just act like a #\$%#ing hardass and order people around? Bad news for you, #\$%#face, but tonights the night your luck runs out. You #\$%#ing tell ANYBODY on these forums what to do again, and you're going to find out the hard way what a #\$%#ing baseball bat to the side of the skull feels like. Think I'm #\$%#ing kidding? I have your IP, I know who you are, and Im more than willing to settle this argument face to #\$%#ing face. You call yourself "Hooligan"? We'll see who's the hooligan when one of us is lying face down in a pile of their own blood, shit, and piss. Try and order someone else on here around, and see what #\$%#ing happens to you. I'm normally a calm guy but when I need to, I'm willing to break some #\$%#ing face to get my point across, just #\$%#ing test me you worthless sack of excrement.

9. #9
LAWLZ!!