The mass of a radioactive substance decreases to half its value every 125 days. What would be the mass of a 500 g sample after 2 years?
2007-03-05 02:57:13 · 5 answers · asked by Count C 1 in Science & Mathematics ➔ Mathematics
2 y / 125 days = 5.84
mass later = mass begin x 2^(-t / T)
mass later = 500 gram x 2^-5.84 = 500 g x 0.01746 = 8.73 gram
Th
2007-03-05 03:35:24 · answer #1 · answered by Thermo 6 · 0⤊ 0⤋
To answer this question,
First, There are 5.84 125days in 2 years
So after one period of 125 days the mass of the substance is calculated by,
500-(50/100)*500, factorized that gives; 500(1-0.5).
For 2 periods of 125 days, 500(1-0.5)^2;
Therefore for 5.84 periods of 125 days;
500(1-0.5)^5.84
=500(0.5^5.84)
=8.72g
2007-03-05 03:17:29 · answer #2 · answered by Shaheed 1 · 0⤊ 0⤋
7. 8125 grams.
There's 365.25 days in a year.
There would be 730.5 days in two years because 365.25 (days) x 2 (years.)
You divide 730.5 by 125 because that's when you know the substance decreases to its half value. That'd be 5.844 - if you round it to the nearest digit, that'd be 6.
500 / 2 to the power of 6 = 7.8125.
Rounded to the nearest digit is 8. :)
2007-03-05 03:07:57 · answer #3 · answered by Nightwolf 4 · 0⤊ 0⤋
500(0.5)^(2*365/125) = 8.7288 g
-----------
Assume the two years are 365 day non leap years.
2007-03-05 03:02:04 · answer #4 · answered by sahsjing 7 · 0⤊ 0⤋
m/2=me^-kt
.5=e^-125k
ln .5 = ln e^-125k
ln .5 = -125k
k = - ln(.5)/125=.0055
m = 500e^-.0055*730
m =500e^-4.015 = 9.02 grams
2007-03-05 03:13:02 · answer #5 · answered by ironduke8159 7 · 0⤊ 0⤋