I think I have this problem almost solved but I am stuck in some areas.
Andrew measures the amount of a very unstable substance to be 100 moles. The half-life of this substance is 3 days (after 3 days, half is gone).
1. Write an exponential function that models this situation where, y, is the
amount of substance and ,x, is time in days. I have y = 100(.5) ^x/3
2. Complete this table: " Days " "Amount"
-3(3 days earlier) 200
3. If the table is correct, how is this information then shown on a graph
to graph the above equation? (Is my equation correct?)
4. Then how would I show the calculation and consider the trend of
the graph if I calculated the expected amount of substance if Andrew
had taken his measurement 9 days earlier?
2 Answers | Add Yours
To calculate the expected amount of substance if Andrew had taken his measurement 9 days earlier, substitute x=-9 in the original equation i.e `y=100*(1/2)^(x/3).`
So, the equation would look like this:
Now simplify to get the expected amount of substance i.e:
An exponential decay process can be described by the formula `N(t)=N_0(1/2)^(t/t_(1/2))` where `N_0` is the initial quantity of the substance that will decay, `N(t)` is the quantity that still remains and has not yet decayed after a time `t` , and `t_(1/2)` is the half-life of the decaying quantity.
The half life of the substance is 3 days and the initial amount is 100 moles.
Considering, y, is the amount of substance and ,x, is time in days, the exponential function that models the situation is `y=100*(1/2)^(x/3)` .
To determine the amount of substance at any moment of time, after it was initially measured or before it, substitute the value of x in the formula.
For instance 3 days earlier, the amount of substance would have been
So, the above table is correct. The values at the other instances of time can be estimated in a similar way.
The graph of the amount of substance versus time elapsed is:
How do I calculate the expected amount of substance if Andrew had taken his measurement 9 days earlier? What would the equation look like?
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