science
posted by matt .
suppose you have 100grams of radioactive plutonium239 with a halflife of 24,000 years. how many grams of plutonium239 will remain after:
A)12,000 years
B)24,000 years
C)96,000 years
how do i do this??????

science 
DrBob222
Here is how you do the first one.
k = 0.693/t_{1/2}
Substitute 24,000 for t_{1/2} in the above equation and calculate k. Then substitute k into the following equation.
ln(No/N) = kt
No = 100 grams = what you start with.
N = what you end up with and this is the unknown.
k from above.
Solve for N.
Use the same procedure for parts B and C. The answer for N will be in grams since No is in grams.
Post your work if you get stuck. 
science 
DrBob222
t in the second equation is, of course, the time which for part a is 12,000, part b is 24,000, etc.

science 
Food4thought...
Well, there would be 50 grams left after 24,000 years. And if you divide both by two, you get __grams(try that yourself!) after 12,000 years. And, if you multiply that (1st problem I did) by 2, you get __grams after 96,000 years. Notice that everything is a multiple of 2.
Hope that helps!
Let me know what answers you got for the A and C (I gave you the answer for B), and I'll tell you if you're right! :) 
science 
DrBob222
Food4thought needs to rethink the answers s/he gave. The answer for 24,000 years (part B) is correct. I don't understand the answer for part A (12,000 years) and the answer for part C gives the same amount (2 x 50 = 100 g) we started with so it CAN'T be correct. Not much truth and little reality in these answers. (Sorry, I couldn't resist.)
Respond to this Question
Similar Questions

calculus
Question: "Plutonium isotope Pu239 has a halflife of 24,100 years. Suppose that 10 grams of Pu239 was released in the Chernobyl nuclear accident. How long will it take for the 10 grams to decay to 1 gram? 
Math Analysis
31. Radioactive decay of material is determined using the formula N = Noe^kt. Find the constant k for Plutonium239 given that its halflife is 24,390 years. ==> I don't really get where to start here because the problem does not … 
Physics
Suppose you have 100 g of radioactive plutonium239 with a halflife of 24,000 years. How many grams will remain after (a) 12,000 years (b) 24,000 years (c) 96,000 years? 
Physics
Suppose you have 100 g of radioactive plutonium239 with a halflife of 24,000 years. How many grams will remain after (a) 12,000 years (b) 24,000 years (c) 96,000 years? 
CHEMISTRY
Suppose you had a detection device that could count every decay event from a radioactive sample of plutonium239.052156 (t1/2 is 24,000 yr). How many counts per second would you obtain from a sample containing 0.126 g of plutonium239? 
Math
_The_Natural_Base_e_ An accident in 1986 at the Chernobyl nuculear plant in the Ukraine released a large amount of plutonium (Pu239)into the atmosphere. The halflife of Pu239 is about 24,110 years. Find the decay constant. Use the … 
Economics
Given the following data, use present worth analysis to ﬁnd the best alternative, A,B, or C. A B C Initial cost $10,000 15,000 $12,000 Annual beneﬁt 6,000 10,000 5,000 Salvage value 1,000 −2,000 3,000 Useful life … 
Math
1. If one wishes to accumulate a 30,000fund in 5 years, how much should he deposit now at 18% compounded quarterly? 
Chemistry
If the half life of Pu239 is 2.4 x 10^4 years, how many years are required for a 20gram sample of plutonium239 to be reduced to a mass of 5 grams? 
Math
Plutonium239 has a halflife of 24 000 years. What percent of plutonium239 remains after 10 000 years?