QuestionMay 24, 2025

The half-life of a radioactive substance is 34.9 years. a. Find the exponential decay model for this substance. b. How long will it take a sample of 500 grams to decay to 400 grams? c. How much of the sample of 500 grams will remain after 10 years?

The half-life of a radioactive substance is 34.9 years. a. Find the exponential decay model for this substance. b. How long will it take a sample of 500 grams to decay to 400 grams? c. How much of the sample of 500 grams will remain after 10 years?
The half-life of a radioactive substance is 34.9 years.
a. Find the exponential decay model for this substance.
b. How long will it take a sample of 500 grams to decay to 400 grams?
c. How much of the sample of 500 grams will remain after 10 years?

Solution
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Answer

a. N(t) = 500 e^{-\frac{\ln(2)}{34.9}t} ### b. Approximately 11.7 years ### c. Approximately 435.6 grams Explanation 1. Determine the decay constant The decay constant k is found using the formula for half-life: **k = \frac{\ln(2)}{t_{1/2}}**. Here, t_{1/2} = 34.9 years. So, k = \frac{\ln(2)}{34.9}. 2. Write the exponential decay model The model is given by **N(t) = N_0 e^{-kt}**, where N_0 is the initial amount. Substitute k from Step 1 to get the model. 3. Calculate time to decay from 500g to 400g Use the decay model: 400 = 500 e^{-kt}. Solve for t: t = \frac{\ln(\frac{400}{500})}{-k}. 4. Calculate remaining amount after 10 years Use the decay model: N(10) = 500 e^{-k \cdot 10} to find the remaining amount after 10 years.

Explanation

1. Determine the decay constant<br /> The decay constant $k$ is found using the formula for half-life: **$k = \frac{\ln(2)}{t_{1/2}}$**. Here, $t_{1/2} = 34.9$ years. So, $k = \frac{\ln(2)}{34.9}$.<br /><br />2. Write the exponential decay model<br /> The model is given by **$N(t) = N_0 e^{-kt}$**, where $N_0$ is the initial amount. Substitute $k$ from Step 1 to get the model.<br /><br />3. Calculate time to decay from 500g to 400g<br /> Use the decay model: $400 = 500 e^{-kt}$. Solve for $t$: $t = \frac{\ln(\frac{400}{500})}{-k}$.<br /><br />4. Calculate remaining amount after 10 years<br /> Use the decay model: $N(10) = 500 e^{-k \cdot 10}$ to find the remaining amount after 10 years.
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