The half-life of a certain radioactive sub- stance is 8 hrs. There are 5 grams present initially. Which of the following gives the best approximation when there will be 1 gram remaining?
2 answers
Would you use the population growth equation?
you would need the decay equation
I would use
amount = 5(1/2)^(t/8), where t is in hours
1 = 5(.5)^(t/8)
.2 = .5^(t/8)
take log of both sides and use log rules
log .2 = (t/8)log .5
t/8 = log .2/log .5 = 2.3219....t = 18.57 hours or appr 3 hours
check:
after 8 hours you would 2.5 g left
after 16 hours you would have 1.25 g left
3 hours to go to get to 1 g ?? , seems reasonable
I would use
amount = 5(1/2)^(t/8), where t is in hours
1 = 5(.5)^(t/8)
.2 = .5^(t/8)
take log of both sides and use log rules
log .2 = (t/8)log .5
t/8 = log .2/log .5 = 2.3219....t = 18.57 hours or appr 3 hours
check:
after 8 hours you would 2.5 g left
after 16 hours you would have 1.25 g left
3 hours to go to get to 1 g ?? , seems reasonable
3 answers