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4.3 Exponential Decay

4.3 Exponential Decay
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  • 1. Exponential Decay of a Glacier

    The size of a glacier is measured in the same way as land, in acres or hectares. In 1900, the size of a glacier was about 320 hectares. Between 1900 and 2000, its size decreased by about 14% per decade.

    Write a formula that represents the size of the glacier at the beginning of each decade from 1900 to 2000.(See Example 1 and Example 2.)

    • Worked-Out Solution

      Use the general formula for exponential decay.

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     __   __   _    _      _____    _____     _____   
     \ \\/ // | || | ||   / ___//  |  ___||  / ____|| 
      \   //  | || | ||   \___ \\  | ||__   / //---`' 
      / . \\  | \\_/ ||   /    //  | ||__   \ \\___   
     /_//\_\\  \____//   /____//   |_____||  \_____|| 
     `-`  --`   `---`   `-----`    `-----`    `----`  
                                                      
    
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    Guest   1 decade ago |
    The photos on page 180 are shocking. How can people see photos like this a wonder about whether global warming is true or not?
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  • 2. Glaciers

    The size of a glacier is measured in the same way as land, in acres or hectares. In 1900, the size of a glacier was about 320 hectares. Between 1900 and 2000, its size decreased by about 14% per decade. Make a table showing the size of the glacier at the beginning of each decade from 1900 to 2000. (See Example 1 and Example 2.)

    A spreadsheet is available to help you complete this exercise.

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      _  _    _    _     _  _      ___     _____    
     | \| || | || | ||  | \| ||   / _ \\  |  __ \\  
     |  ' || | || | ||  |  ' ||  | / \ || | |  \ || 
     | .  || | \\_/ ||  | .  ||  | \_/ || | |__/ || 
     |_|\_||  \____//   |_|\_||   \___//  |_____//  
     `-` -`    `---`    `-` -`    `---`    -----`   
                                                    
    
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  • 3. Decrease in Area of a Glacier

    The size of a glacier is measured in the same way as land, in acres or hectares. In 1900, the size of a glacier was about 320 hectares. Between 1900 and 2000, its size decreased by about 14% per decade. Sketch a graph showing the decrease in the area of the glacier from 1900 to 2000. (See Example 1 and Example 2.)

    A spreadsheet is available to help you complete this exercise.

    • Worked-Out Solution

      The formula from Exercise 1 is

      By entering this into a spreadsheet, you can draw the following graph.

      data folder

      Study Tip

         1 square mile = 1 section = 4 quarters = 640 acres

         1 hectare = 10,000 aquare meters

         1 hectare = 2.47 acres

         1 acre = 43,560 square feet (a square about 209 ft on each side)

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      _____      ___      ______   __   __  __    __  
     |__  //    / _ \\   /_   _//  \ \\/ // \ \\ / // 
       / //    / //\ \\    | ||     \ ` //   \ \/ //  
      / //__  |  ___  ||  _| ||      | ||     \  //   
     /_____|| |_||  |_|| /__//       |_||      \//    
     `-----`  `-`   `-`  `--`        `-`'       `     
                                                      
    
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  • 4. Estimating Area of a Glacier

    The size of a glacier is measured in the same way as land, in acres or hectares. In 1900, the size of a glacier was about 320 hectares. Between 1900 and 2000, its size decreased by about 14% per decade. Use the graph in Exercise 3 to estimate the area of the glacier in 2000. (See Example 1 and Example 2.)

    A spreadsheet is available to help you complete this exercise.

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      ______   __   __   _    _    _    _     ______  
     /_   _//  \ \\/ // | \  / || | || | ||  /_   _// 
     `-| |,-    \ ` //  |  \/  || | || | ||  `-| |,-  
       | ||      | ||   | .  . || | \\_/ ||    | ||   
       |_||      |_||   |_|\/|_||  \____//     |_||   
       `-`'      `-`'   `-`  `-`    `---`      `-`'   
                                                      
    
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  • 5. Glacier

    The size of a glacier is measured in the same way as land, in acres or hectares. In 1900, the size of a glacier was about 320 hectares. Between 1900 and 2000, its size decreased by about 14% per decade. A general rule is that a moving piece of ice and snow is called a glacier when its size is at least 10 hectares. Assuming the trend continues, when will the glacier be too small to be considered a glacier? ( See Example 1 and Example 2.)

    A spreadsheet is available to help you complete this exercise.

    • Worked-Out Solution

      The formula from Exercise 1 is

      A spreadsheet using this formula is shown below.

      data folder

      From the spreadsheet, you can see that the size will be too small to be classified as a glacier around 2130.

      Study Tip

         1 square mile = 1 section = 4 quarters = 640 acres

         1 hectare = 10,000 aquare meters

         1 hectare = 2.47 acres

         1 acre = 43,560 square feet (a square about 209 ft on each side)

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       _____     ___                ______            
      / ___//   / _ \\    ____     /_   _//     ___   
      \___ \\  | / \ ||  |    \\    -| ||-     /   || 
      /    //  | \_/ ||  | [] ||    _| ||_    | [] || 
     /____//    \___//   |  __//   /_____//    \__ || 
    `-----`     `---`    |_|`-`    `-----`      -|_|| 
                         `-`                     `-`  
    
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  • 6. Size of a Glacier

    The size of a glacier is measured in the same way as land, in acres or hectares. In 1900, the size of a glacier was about 320 hectares. Between 1900 and 2000, its size decreased by about 14% per decade. Suppose that a recent study predicts that the glacier will be completely melted by 2040. (See Example 1 and Example 2.)

    1. Does this prediction agree with your answer in Exercise 5? What does the research suggest about the melting rate of the glacier after 2000?
    2. When do you think an exponential model would be appropriate to model glacial melting? When do you think a linear model would be appropriate? Explain.
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      ______     ___                _____      _____  
     /_   _//   / _ \\      ___    |  ___||   / ___// 
     `-| |,-   | / \ ||    /   ||  | ||__     \___ \\ 
       | ||    | \_/ ||   | [] ||  | ||__     /    // 
       |_||     \___//     \__ ||  |_____||  /____//  
       `-`'     `---`       -|_||  `-----`  `-----`   
                             `-`                      
    
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