For all of the remaining questions, show or describe your work. 3. The mass of a sample of a mystery element is measured periodically as it decays. If 0.78 % of the sample remains after 100 days, what is the half-life of the element?

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**Problem 3:**

For all of the remaining questions, show or describe your work.

3. The mass of a sample of a mystery element is measured periodically as it decays. If 0.78% of the sample remains after 100 days, what is the half-life of the element?

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**Explanation for Students:**

This problem asks you to determine the half-life of an unknown element based on its decay over time. The concept of half-life is critical in understanding radioactive decay, as it represents the time required for half of the substance to decay.

**Calculation Steps:**

1. **Initial Setup:**
   - Let the initial mass be \( M_0 \).
   - After 100 days, 0.78% of \( M_0 \) remains.

2. **Decay Formula:**
   - Use the exponential decay formula:  
     \[ N(t) = N_0 \left( \frac{1}{2} \right)^{t / T_{1/2}} \]  
     where:
     - \( N(t) \) is the remaining amount after time \( t \),
     - \( N_0 \) is the initial amount,
     - \( T_{1/2} \) is the half-life of the substance.

3. **Substitute Known Values:**
   - \( 0.0078 \times M_0 = M_0 \left( \frac{1}{2} \right)^{100 / T_{1/2}} \)

4. **Solve for Half-Life \( T_{1/2} \):**
   - Simplify the equation to solve for \( T_{1/2} \).

This exercise is an application of mathematical modeling using exponential functions to describe physical phenomena. It requires algebraic manipulation and understanding of logarithms to solve for the unknown half-life.
Transcribed Image Text:**Problem 3:** For all of the remaining questions, show or describe your work. 3. The mass of a sample of a mystery element is measured periodically as it decays. If 0.78% of the sample remains after 100 days, what is the half-life of the element? --- **Explanation for Students:** This problem asks you to determine the half-life of an unknown element based on its decay over time. The concept of half-life is critical in understanding radioactive decay, as it represents the time required for half of the substance to decay. **Calculation Steps:** 1. **Initial Setup:** - Let the initial mass be \( M_0 \). - After 100 days, 0.78% of \( M_0 \) remains. 2. **Decay Formula:** - Use the exponential decay formula: \[ N(t) = N_0 \left( \frac{1}{2} \right)^{t / T_{1/2}} \] where: - \( N(t) \) is the remaining amount after time \( t \), - \( N_0 \) is the initial amount, - \( T_{1/2} \) is the half-life of the substance. 3. **Substitute Known Values:** - \( 0.0078 \times M_0 = M_0 \left( \frac{1}{2} \right)^{100 / T_{1/2}} \) 4. **Solve for Half-Life \( T_{1/2} \):** - Simplify the equation to solve for \( T_{1/2} \). This exercise is an application of mathematical modeling using exponential functions to describe physical phenomena. It requires algebraic manipulation and understanding of logarithms to solve for the unknown half-life.
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