AP Physics 2 › Quantum and Nuclear Physics
Suppose that the half-life of substance A is known to be . When substance A decays, it becomes substance B. If this is the only way that substance B can be produced, and a sample is found that contains
of substance A and
of substance B, what is the age of this sample?
To find the approximate age of the sample, we need to consider the half-life of the starting material, substance A. We also need to consider the relative amounts of substance A and substance B.
Since we are told that the sample we are looking at contains substance A and
substance B, we know that the sample must have started out with
of substance A. Furthermore, in order to go from
to
, we know that a total of two half-lives must have passed. And since we know that one half-life is equal to
, we can conclude that a total of
must have passed.
Suppose that the half-life of substance A is known to be . When substance A decays, it becomes substance B. If this is the only way that substance B can be produced, and a sample is found that contains
of substance A and
of substance B, what is the age of this sample?
To find the approximate age of the sample, we need to consider the half-life of the starting material, substance A. We also need to consider the relative amounts of substance A and substance B.
Since we are told that the sample we are looking at contains substance A and
substance B, we know that the sample must have started out with
of substance A. Furthermore, in order to go from
to
, we know that a total of two half-lives must have passed. And since we know that one half-life is equal to
, we can conclude that a total of
must have passed.
The half-life of carbon-14 is 5730 years.
Rex the dog died in 1750. What percentage of his original carbon-14 remained in 1975 when he was found by scientists?
225 years have passed since Rex died. Find the number of half-lives that have elapsed.
To find the proportion of a substance that remains after a certain number of half-lives, use the following equation:
Here, is the number of half lives that have elapsed.
Suppose that the half-life of substance A is known to be . When substance A decays, it becomes substance B. If this is the only way that substance B can be produced, and a sample is found that contains
of substance A and
of substance B, what is the age of this sample?
To find the approximate age of the sample, we need to consider the half-life of the starting material, substance A. We also need to consider the relative amounts of substance A and substance B.
Since we are told that the sample we are looking at contains substance A and
substance B, we know that the sample must have started out with
of substance A. Furthermore, in order to go from
to
, we know that a total of two half-lives must have passed. And since we know that one half-life is equal to
, we can conclude that a total of
must have passed.
The half-life of carbon-14 is 5730 years.
Rex the dog died in 1750. What percentage of his original carbon-14 remained in 1975 when he was found by scientists?
225 years have passed since Rex died. Find the number of half-lives that have elapsed.
To find the proportion of a substance that remains after a certain number of half-lives, use the following equation:
Here, is the number of half lives that have elapsed.
The half-life of carbon-14 is 5730 years.
Rex the dog died in 1750. What percentage of his original carbon-14 remained in 1975 when he was found by scientists?
225 years have passed since Rex died. Find the number of half-lives that have elapsed.
To find the proportion of a substance that remains after a certain number of half-lives, use the following equation:
Here, is the number of half lives that have elapsed.
A scientist discovers a new radioactive nuclei. She runs a test on a sample and finds it has an activity of .
later, it has an activity of
.
Determine the activity after the original reading.
None of these
There will be no activity left
Using the relationship:
Here, is the activity at a given time,
is the intial activity,
is the radioactive decay constant, and
is the time passed since the initial reading.
Rearranging the equation to solve for .
Converting minutes to seconds and plugging in values.
Again using the relationship
Using the new
A long rod is traveling at
in relationship to an observer along it's long axis. Determine the observed length.
None of these
Using
Plugging in values
Determine the observed length of a rod traveling along it's long axis at
in relation to an observer.
None of these
Use the following equation:
Where is the rest length,
is the velocity of the object
is the speed of light
is the observed length
Plugging in values
Determine the observed length of a rod traveling along it's long axis at
in relation to an observer.
None of these
Use the following equation:
Where is the rest length,
is the velocity of the object
is the speed of light
is the observed length
Plugging in values