Question

If 8 g of a radioactive substance are present initially and 3 yr later only 4 g remain, how much of the substance will be present after 7 yrs?

Answer 1

Hi assume you are familiar with the term half life, which refers to the time it takes for something to reach half of its magnitude. In this case we can’t see that from 8 g originally we get to 4 g which is the half of it in 3 years. With all this information we can proceed to use the half life formula to calculate the amount of substance that will be present after 7 years.

The half-life formula states:


N(t) = initialPopulation * (0.5) ^ (expectedTime/half-lifeTime)

So:

N(7) = 8 * (0.5) ^ 7/3
N(7) = 1.587 g

There is presence of 1.587 g of radioactive substance 7 years later.