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?

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.

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

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)

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