Question 925599
Hi!!!!! I tried attempting this really hard problem on a homework assignment and I have no clue what i'm doing wrong, it's a half life question and i keep getting the wrong sort of answer, I hope you're ready :D "An accident in 1986 at Cherynobyl play in the Ulraine released a large amount of plutonium (Pu-239) into the atmosphere. The half-life of Pu-239 is about 24,110 years.

a) Find the decay constant
b) Use the function N(t) = N0e^-kt to find what remains of an initial 20 grams of Pu-239 after 5000 years.
c) How long will it take for these 20 grams to decay to know gram? Go down to the Years, Days, Hours, Minutes, and Seconds.. I got A! so that won't be a problem, maybe you could try and solve it too? I got a weird number for b - 17.3? Is that odd? I mean... isn't it supposed to go down? And what's the nonsese with c? Any help at all would be great, thanks sO much!
<pre>You did get the correct amount for b), but with the wrong sign. It should be 17.3 gm, and NOT - 17.3 gm.
The reason why you got a - 17.3 is because you used the WRONG formula. The GROWTH/DECAY formula is: {{{highlight_green(matrix(1,7, N(t), "=", N[o]e^(kt), NOT, N(t), "=", N[o]e^(- kt)))}}}
Now, if k < 0, then that signifies DECAY/DECREASE, and k being > 0 signifies GROWTH!
For c), does "know gram" mean NO GRAMS, as in ZERO (0) grams?