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Hourly temperature data for Boulder, Colorado, San Francisco, California, Nantucket, Massachusetts, and Duluth, Minnesota, over a 12 hr period on the same day of January are shown in the figure. Assume that these data are taken from a continuous temperature function \(T(t) .\) The average temperature over the 12 -hr period is \(\bar{T}=\frac{1}{12} \int_{0}^{12} T(t) d t\). Find an accurate approximation to the average temperature over the 12 -hr period for San Francisco. State your method.

Short Answer

Expert verified
Answer: We use the Trapezoidal rule to approximate the average temperature in San Francisco over a 12-hour period. The final equation to calculate the average temperature is \(\bar{T} \approx \frac{1}{12}(T_1 + T_2 + ... + T_{12})\).

Step by step solution

01

Observe the hourly temperature data and choose an appropriate method for approximation

We can choose from several different methods for integration approximation, like the Trapezoidal rule, Simpson's rule, or the Midpoint rule. In the case of hourly temperature data, it is reasonable to assume that the changes in temperature are relatively smooth and regular. Thus, we can use the Trapezoidal rule or Simpson's rule for this problem. For simplicity, let's use the Trapezoidal rule.
02

Set up the Trapezoidal rule

The Trapezoidal rule approximates an integral by calculating the area of a series of trapezoids. The average temperature over the 12-hour period can be approximated as: \(\bar{T} \approx \frac{1}{12} \sum_{i=1}^{n} \frac{(T(t_{i-1})+T(t_i))}{2}\Delta t\), where \(n\) is the number of data points (in this case, hourly temperature readings), \(t_i\) are the time values, and \(\Delta t\) is the time interval between consecutive readings (here \(\Delta t = 1\) hour).
03

Calculate the Trapezoidal sum for San Francisco's temperature data

Plug in the San Francisco's hourly temperature data into the equation we derived in step 2: \(\bar{T} \approx \frac{1}{12} \sum_{i=1}^{12} \frac{(T(t_{i-1}) + T(t_i))}{2}\Delta t\) Remember that the temperature data is not provided in the text of the problem. Let's assume that the hourly temperature values for San Francisco are \(T_1, T_2, ..., T_{12}\). Then plug these values into the equation and compute the sum: \(\bar{T} \approx \frac{1}{12}\Big(\frac{(T_1+T_2)}{2}+\frac{(T_2+T_3)}{2}+...+\frac{(T_{11}+T_{12})}{2}\Big)\)
04

Calculate the average temperature for San Francisco

Evaluate the equation obtained in step 3: \(\bar{T} \approx \frac{1}{12}(T_1 + T_2 + ... + T_{12})\) The final result will be an accurate approximation for the average temperature in San Francisco over the 12-hour period. Depending on the temperature values, you can find \(\bar{T}\).

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Trapezoidal Rule
The Trapezoidal Rule is a numerical method used to approximate the definite integral of a function. It is particularly useful when the function can't be easily integrated analytically. This method works by dividing the area under the curve into trapezoids rather than rectangles, hence its name.
The formula for the Trapezoidal Rule is:
  • For one segment between two points, it is \[\frac{(T(t_{i-1}) + T(t_i))}{2} \times \Delta t\]
    Here, \(T(t_i)\) are the temperature values at different times, and \(\Delta t\) is the time interval between measurements.
Using this approach, each pair of sequential temperature readings forms the two parallel sides of a trapezoid. By multiplying the average of these two temperatures by the time interval, we get the area of each trapezoid.
Finally, by adding up all these trapezoidal areas across the given period, you derive an approximate total integral for the temperature function over the entire interval.
Average Temperature
Average temperature over a given period gives us a single value representative of the entire set of temperature data. When we talk about average temperature, it is often calculated over a specific range of time.
To find the average temperature over a 12-hour period, you would integrate the temperature function over the time (12 hours) and then divide by the total time:
\[\bar{T} = \frac{1}{12} \int_{0}^{12} T(t) dt \]
Where \( \bar{T} \) is the average temperature, and \( T(t) \) is the continuous temperature function. This calculation requires determining the total "area" under the temperature curve across the specified period and then averaging that area.
Using numerical methods like the Trapezoidal Rule can give us this average when we don't have a simple function for \( T(t) \) but instead have discrete data points, such as hourly temperatures.
Continuous Temperature Function
A continuous temperature function \( T(t) \) represents how temperature changes over time continuously, rather than in discrete steps. In an ideal scenario, this function would allow us to predict the temperature at any given moment without needing to check individual hourly records.
In practice, however, we often deal with real-world data, which may be provided at intervals such as hourly. The assumption of a continuous function helps in simplifying complex computations and making accurate predictions using available numerical methods.
  • When assumptions about continuity are correct, it leads to smoother approximations and logical predictions over the period in question.
For instance, in calculating the average temperature of San Francisco over 12 hours, recognizing the temperature as continuous allows us to use the Trapezoidal Rule effectively. It makes the transformation of discrete data into a continuous perspective, helping us get meaningful insights such as mean temperature values over time.
By understanding that the temperature changes aren't abrupt but transition smoothly, we can allocate confidence in our approximations and theoretically can interpolate values between given data points.

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Most popular questions from this chapter

Explain how to solve a separable differential equation of the form \(g(y) y^{\prime}(t)=h(t)\).

Determine whether the following statements are true and give an explanation or counterexample. a. The Trapezoid Rule is exact when used to approximate the definite integral of a linear function. b. If the number of subintervals used in the Midpoint Rule is increased by a factor of \(3,\) the error is expected to decrease by a factor of 8. c. If the number of subintervals used in the Trapezoid Rule is increased by a factor of \(4,\) the error is expected to decrease by a factor of 16.

Apply Simpson's Rule to the following integrals. It is easiest to obtain the Simpson's Rule approximations from the Trapezoid Rule approximations, as in Example \(7 .\) Make \(a\) table similar to Table 7.8 showing the approximations and errors for \(n=4,8,16,\) and \(32 .\) The exact values of the integrals are given for computing the error. \(\int_{0}^{\pi} e^{-t} \sin t d t=\frac{1}{2}\left(e^{-\pi}+1\right)\)

Compare the errors in the Midpoint and Trapezoid Rules with \(n=4,8,16,\) and 32 subintervals when they are applied to the following integrals (with their exact values given). \(\int_{0}^{\pi} \ln (5+3 \cos x) d x=\pi \ln \frac{9}{2}\)

An open cylindrical tank initially filled with water drains through a hole in the bottom of the tank according to Torricelli's Law (see figure). If \(h(t)\) is the depth of water in the tank for \(t \geq 0,\) then Torricelli's Law implies \(h^{\prime}(t)=2 k \sqrt{h}\), where \(k\) is a constant that includes the acceleration due to gravity, the radius of the tank, and the radius of the drain. Assume that the initial depth of the water is \(h(0)=H\). a. Find the general solution of the equation. b. Find the solution in the case that \(k=0.1\) and \(H=0.5 \mathrm{m}\). c. In general, how long does it take the tank to drain in terms of \(k\) and \(H ?\)

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