A food worker has cooled a pot of soup from 135°F to 70°F (57°C to 21°C) in 2 hours. How long do they have to cool it from 70°F to 41°F (21°C to 5°C)?

A. 1 hour
B. 2 hours
C. 4 hours
D. 6 hours



Answer :

Let's solve the problem step by step:

1. Initial Condition Understanding:
- The temperature was initially [tex]\(135^\circ F\)[/tex] and it was cooled to [tex]\(70^\circ F\)[/tex] in 2 hours.
- Now we need to find out how long it will take to cool the soup from [tex]\(70^\circ F\)[/tex] to [tex]\(41^\circ F\)[/tex].

2. Temperature Differences:
- The initial temperature drop from [tex]\(135^\circ F\)[/tex] to [tex]\(70^\circ F\)[/tex] is [tex]\(135 - 70 = 65^\circ F\)[/tex].
- The new temperature drop we need to work with is from [tex]\(70^\circ F\)[/tex] to [tex]\(41^\circ F\)[/tex], which is [tex]\(70 - 41 = 29^\circ F\)[/tex].

3. Exponential Cooling Behavior:
- The cooling process behaves exponentially, and the time required for cooling can be related to the temperature drop proportionally.

4. Proportional Calculation:
- Given that the initial cooling of [tex]\(65^\circ F\)[/tex] took 2 hours, we need to find the time [tex]\(t\)[/tex] for a cooling of [tex]\(29^\circ F\)[/tex].
- The time required for the second cooling is proportional to the ratio of the temperature drops.
- Therefore, the time [tex]\(t\)[/tex] can be calculated using the proportion:
[tex]\[ \frac{t}{2 \text{ hours}} = \frac{29^\circ F}{65^\circ F} \][/tex]

5. Solve for [tex]\(t\)[/tex]:
[tex]\[ t = 2 \text{ hours} \times \frac{29^\circ F}{65^\circ F} = 2 \times \frac{29}{65} = 2 \times 0.4461538461538462 = 0.8923076923076924 \text{ hours} \][/tex]

6. Rounding the Time:
- We need to round the time to the nearest whole number.
- [tex]\(0.8923076923076924\)[/tex] hours rounded to the nearest whole number is 1 hour.

Hence, the food worker will need approximately 1 hour to cool the soup from [tex]\(70^\circ F\)[/tex] to [tex]\(41^\circ F\)[/tex].

The correct answer is: 1 hour.