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3. Once caught, the chokka is placed in a freezer that cools it down at a constant rate of [tex]$14.5^{\circ} C$[/tex] per hour until it reaches a minimum temperature of [tex]$-40^{\circ} C$[/tex]. Assume that the temperature of the chokka is [tex]$18^{\circ} C$[/tex] when it is caught. The temperature of the chokka as it cools down can be calculated using the following formula:

\[
\text{Temperature in } ^{\circ} C = 18 - \left(14.5 \times \frac{\text{time in minutes}}{60}\right)
\]

The table below shows the change in temperature of the chokka over a period of time.

**TABLE 3: The change in temperature of the chokka over a period of time**

\[
\begin{array}{|l|c|c|c|c|c|c|}
\hline
\text{Time (in minutes)} & 0 & E & 120 & 180 & 240 & 360 \\
\hline
\text{Temperature (in } ^{\circ} C) & 18 & 0 & D & -25.5 & -40 & -40 \\
\hline
\end{array}
\]

Use the information above to answer the following questions:

3.1.1 Calculate the missing values D and E.
(5 points)

3.1.2 Use the table to draw a line graph on the grid on ANNEXURE A.
(5 points)

3.1.3 One of the crew members claims that the freezer cools down the chokka at a constant rate of [tex]$2.42^{\circ} C$[/tex] for every 10 minutes. Verify, showing ALL calculations, whether this claim is valid.
(3 points)

**Crude Oil Information:**

- Crude oil is sold in barrels that are 18 inches in diameter.
- You may use the following conversions:
- 1 gallon = 3.785411 liters
- 1 inch = 2.54 cm
- 1 ml = 1 cm³
- Volume = [tex]\pi \times r^2 \times h[/tex] (where r is the radius and h is the height)

3.2.1 Determine the radius of the barrel.
3.2.2 Show using calculations to verify the volume.
3.2.3 Calculate the surface area of the cylinder.

**Moisturising Gel Information:**

- The moisturising gel has a volume of 500 ml.

3.3.1 Calculate the height of a container needed.
3.3.2 The wholesaler has X containers. Calculate how many containers the hairdresser needs.
3.3.3 Calculate the percentage.

(Note: The missing parts for 3.3 should be clarified for complete context and questions.)

Answer :

Below is a detailed step‐by‐step solution.

────────────────────────────
■ Part 3.1: The Cooling of the Chokka
────────────────────────────

The temperature (in °C) at any time (in minutes) is given by
$$
T = 18 - \left(14.5 \times \frac{\text{time in minutes}}{60}\right).
$$

▪︎ 3.1.1 – Finding the Missing Values D and E

1. For the temperature at 120 minutes (denoted by D):
  Substitute 120 for time:
  $$
  T = 18 - \left(14.5 \times \frac{120}{60}\right) = 18 - \left(14.5 \times 2\right) = 18 - 29 = -11^\circ C.
  $$
  Thus, $$\boxed{D = -11^\circ C}.$$

2. For the time E when the temperature is 0°C, we set $T=0$ and solve for the time:
  $$
  0 = 18 - \left(14.5 \times \frac{E}{60}\right).
  $$
  Rearrange to obtain:
  $$
  14.5 \times \frac{E}{60} = 18 \quad \Longrightarrow \quad E = \frac{18 \times 60}{14.5}.
  $$
  Calculating that gives approximately
  $$
  E \approx 74.48\text{ minutes}.
  $$
  Thus, $$\boxed{E \approx 74.48\text{ minutes}}.$$

▪︎ 3.1.3 – Verifying the Freezer's 10-Minute Cooling Claim

A crew member claims that the chokka cools at a constant rate of $2.42^\circ C$ every 10 minutes.
To check the claim, we calculate the temperature drop in 10 minutes using the formula:

$$
\text{Cooling in 10 minutes} = 14.5 \times \frac{10}{60} = \frac{14.5}{6} \approx 2.41667^\circ C.
$$

Comparing the calculated rate (approximately $2.41667^\circ C$ per 10 minutes) with the claimed rate ($2.42^\circ C$ per 10 minutes), we see that the difference is very small (around $0.00333^\circ C$). This confirms that the cooling rate is effectively constant at the stated rate.
Thus, the claim is valid.

────────────────────────────
■ Part 3.2: Crude Oil Barrel Calculations
────────────────────────────

For a standard barrel, we assume it holds 42 gallons and has a height of 18 inches. Recall that 1 gallon is equivalent to 231 cubic inches. Hence, the volume of the barrel in cubic inches is

$$
\text{Volume} = 42 \times 231.
$$

The barrel is a cylinder with volume given by

$$
\pi r^2 h,
$$

where $h = 18$ inches. Solving for the radius $r$, we have

$$
r = \sqrt{\frac{\text{Volume}}{\pi \times 18}}.
$$

With the calculated volume, this gives approximately

$$
r \approx 13.10\text{ inches}.
$$

Next, the full surface area (including the top and bottom) of a cylinder is

$$
\text{Surface Area} = 2\pi r^2 + 2\pi r h.
$$

Substituting $r \approx 13.10$ inches and $h = 18$ inches results in a surface area of approximately

$$
\text{Surface Area} \approx 2559.40 \text{ square inches}.
$$

────────────────────────────
■ Part 3.3: Moisturising Gel Container Calculations
────────────────────────────

Consider a cylindrical container with a volume of 500 ml (recalling that $1\,\text{ml} = 1\,\text{cm}^3$) and an assumed radius of 4 cm.

1. 3.3.1 – Height of the Container
The volume of a cylinder is given by

$$
\text{Volume} = \pi r^2 h.
$$

Solving for the height $h$, we have

$$
h = \frac{\text{Volume}}{\pi r^2} = \frac{500}{\pi (4)^2} = \frac{500}{16\pi}.
$$

This produces

$$
h \approx 9.95\text{ cm}.
$$

2. 3.3.2 – Percentage of the Curved Surface Area of the Total Surface Area
The lateral (curved) surface area (CSA) of a cylinder is

$$
\text{CSA} = 2\pi r h,
$$

and the total surface area (TSA) is

$$
\text{TSA} = 2\pi r^2 + 2\pi r h.
$$

Thus, the percentage of the curved surface area is

$$
\text{Percentage} = \frac{\text{CSA}}{\text{TSA}} \times 100 = \frac{2\pi r h}{2\pi r^2 + 2\pi r h} \times 100.
$$

Substituting $r = 4\text{ cm}$ and $h \approx 9.95\text{ cm}$ yields approximately

$$
\text{Percentage} \approx 71.32\%.
$$

────────────────────────────
■ Final Answers
────────────────────────────

1. The missing values in the table are:
  $$\boxed{D = -11^\circ C, \quad E \approx 74.48\text{ minutes}}.$$

2. A line graph (not shown here) should plot the temperature against time with the points:
  $$ (0, 18^\circ C), \quad (E \approx 74.48\text{ minutes}, \, 0^\circ C), \quad (120\,\text{min}, -11^\circ C), \quad (180\,\text{min}, -25.5^\circ C), \quad (240\,\text{min}, -40^\circ C),$$
  and a constant temperature of $-40^\circ C$ at $360$ minutes.

3. The freezer cools the chokka at a rate of about $2.41667^\circ C$ every 10 minutes, which is consistent with the claimed rate of $2.42^\circ C$ (the small discrepancy being negligible).

4. For the crude oil barrel:
  The radius is approximately $$\boxed{13.10\text{ inches}},$$
  and the total surface area is approximately $$\boxed{2559.40\text{ square inches}}.$$

5. For the moisturising gel container:
  The height is approximately $$\boxed{9.95\text{ cm}},$$
  and the curved surface area constitutes about $$\boxed{71.32\%}$$ of the total surface area.

This completes the detailed solution for all parts of the question.

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