Half Life Problem: Solving for 5 Years Starting with 100 Grams

In summary, the problem involves calculating the amount of radioactive material after 5 years if 5 grams are added to it each year, starting with 100 grams and a half-life of 50ln2 years. Using the recursive equation N(t + 1) = (N(t) e^-kt) + 10, the amount after 5 years is calculated by summing up the values for t = 0 to 4. However, there may be an easier method to solve this problem.
  • #1
magnifik
360
0
The problem:
A radioactive material has a half-life of 50ln2 years. If you add 5 grams per year to the material, how much material will you have after 5 years if you start with 100 grams?

What I've done so far:
t = ln2/k = 50ln2
k = 1/50
k = .02
A = A0e^-kt
N = 100e^(-.02)(5) = 90 grams
90 + 5 = 95 grams

i'm not sure if this is correct because i have a feeling this is not the correct way to take into account the 5 grams per year being added constantly. please let me know if i need to fix anything. thx.
 
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  • #2
Calculate mass after a year, add 5. Repeat five times.
 
  • #3


Perhaps it would be easier if you start by writing down a recursive equation, i.e. express the quantity N(t + 1) after one year in terms of the quantity N(t) in the previous year?
 
  • #4
using both suggestions i would have
N(t + 1) = (N(t) e^-kt) + 10
but i would still have to sum up each value from t = 0 to 4
is there an easier way to do this?
 

1. How do you calculate the half-life of a substance?

To calculate the half-life of a substance, you need to know the initial amount of the substance and the rate at which it decays. You can then use the formula: Half-life = ln(2) / decay rate. For example, if the decay rate is 0.05 and the initial amount is 100 grams, the half-life would be 13.86 years.

2. What is the meaning of half-life in a scientific context?

In a scientific context, half-life refers to the amount of time it takes for half of a given substance to decay or break down into a different form. It is a measure of the rate at which a substance decays, and it is often used to determine the stability and potential hazards of radioactive materials.

3. How do you solve for the amount of a substance after a certain number of years using the half-life formula?

To solve for the amount of a substance after a certain number of years using the half-life formula, you can use the following equation: Amount after x years = Initial amount x (1/2)^(x / half-life). For example, if you want to determine the amount of a substance after 5 years starting with 100 grams and the half-life is 10 years, the equation would be: 100g x (1/2)^(5/10) = 70.71 grams.

4. How does the half-life of a substance affect its stability?

The half-life of a substance is directly related to its stability. A substance with a longer half-life is considered more stable, as it takes longer for half of the substance to decay. Conversely, a substance with a shorter half-life is less stable, as it decays at a faster rate.

5. Can the half-life of a substance change over time?

Yes, the half-life of a substance can change over time. Factors such as temperature, pressure, and chemical reactions can all affect the decay rate of a substance, which in turn can alter its half-life. Additionally, some substances have multiple decay pathways, each with their own half-life, making it more complex to determine the overall half-life of the substance.

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