Here is a new twist on the question. Suppose we want to cool our hot coffee to 100 °F as quickly as possible (sooner than 10 minutes). Suppose also that we have 1 ounce of cold milk with a temperature of 40°F that we can add to the 8 ounces of your coffee at any time. We will try to answer the question: When should we add the milk to cool the coffee to 100°F as quickly as possible? 8. We need to make an assumption about the effect of cold milk on the temperature of the coffee. A reasonable assumption is that when milk is added to coffee, the temperature of the coffee immediately decreases to the average of the coffee temperature and the milk temperature, where the average is weighted by the volumes, illustrated in the figure on the right. Milk is added 150. New temperature of coffee (10, 100). As you can see on the graph, adding the milk immediately changes the coffee's temperature. So if we add 1 ounce of milk with temperature Tm to 8 ounces of coffee with temperature T, the temperature of the mixture will be t (time in minutes) 1. Tm + 8· T Tm + 8T Tnew = (2) 1+8 If the milk is added when the temperature of the coffee is 150 °F as shown in the graph, what will be the temperature of the mixture? Does it agree with the graph? T (temperature in F)

Calculus: Early Transcendentals
8th Edition
ISBN:9781285741550
Author:James Stewart
Publisher:James Stewart
Chapter1: Functions And Models
Section: Chapter Questions
Problem 1RCC: (a) What is a function? What are its domain and range? (b) What is the graph of a function? (c) How...
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Solution from 3: T(t) = A + (T0 - A)e^-kt

A = 72 degrees F

k = 0.125

T0 = 170 degrees F

 

Here is a new twist on the question. Suppose we want to cool our hot coffee to 100°F as quickly
as possible (sooner than 10 minutes). Suppose also that we have 1 ounce of cold milk with a
temperature of 40°F that we can add to the 8 ounces of your coffee at any time. We will try to
answer the question: When should we add the milk to cool the coffee to 100°F as quickly as possible?
8. We need to make an assumption about the effect
of cold milk on the temperature of the coffee.
A reasonable assumption is that when milk is
added to coffee, the temperature of the coffee
immediately decreases to the average of the
coffee temperature and the milk temperature,
where the average is weighted by the volumes,
illustrated in the figure on the right.
Milk is added
-150
New temperature of coffee
(10, 100).
As you can see on the graph, adding the milk
immediately changes the coffee's temperature.
So if we add 1 ounce of milk with temperature
T, to 8 ounces of coffee with temperature T,
t (time in minutes)
the temperature of the mixture will be
1. Tm + 8 · T
Tm + 8T
Tnew =
(2)
1+8
9
If the milk is added when the temperature of the coffee is 150 °F as shown in the graph, what
will be the temperature of the mixture? Does it agree with the graph?
T (temperaturein F)
Transcribed Image Text:Here is a new twist on the question. Suppose we want to cool our hot coffee to 100°F as quickly as possible (sooner than 10 minutes). Suppose also that we have 1 ounce of cold milk with a temperature of 40°F that we can add to the 8 ounces of your coffee at any time. We will try to answer the question: When should we add the milk to cool the coffee to 100°F as quickly as possible? 8. We need to make an assumption about the effect of cold milk on the temperature of the coffee. A reasonable assumption is that when milk is added to coffee, the temperature of the coffee immediately decreases to the average of the coffee temperature and the milk temperature, where the average is weighted by the volumes, illustrated in the figure on the right. Milk is added -150 New temperature of coffee (10, 100). As you can see on the graph, adding the milk immediately changes the coffee's temperature. So if we add 1 ounce of milk with temperature T, to 8 ounces of coffee with temperature T, t (time in minutes) the temperature of the mixture will be 1. Tm + 8 · T Tm + 8T Tnew = (2) 1+8 9 If the milk is added when the temperature of the coffee is 150 °F as shown in the graph, what will be the temperature of the mixture? Does it agree with the graph? T (temperaturein F)
We know that adding milk at any point after t; will make the coffee's temperature less than
100°F. What if we add the milk before t;? How much longer will it need to cool? Let's
investigate!
11. Assume the coffee is allowed to cool for tmilk minutes (after which we will add the milk), where
tmilk will be determined later. Use your solution from 3. and the value of k found in 6. and
7. to write down the temperature of the coffee at t = tmilk; call it T*. (Your answer will have
tmilk in it.)
Transcribed Image Text:We know that adding milk at any point after t; will make the coffee's temperature less than 100°F. What if we add the milk before t;? How much longer will it need to cool? Let's investigate! 11. Assume the coffee is allowed to cool for tmilk minutes (after which we will add the milk), where tmilk will be determined later. Use your solution from 3. and the value of k found in 6. and 7. to write down the temperature of the coffee at t = tmilk; call it T*. (Your answer will have tmilk in it.)
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