## anonymous one year ago A 39 gram sample of a substance that's a by-product of fireworks has a k-value of 0.1024. N = N0e -kt N0 = initial mass (at time t = 0) N = mass at time t k = a positive constant that depends on the substance itself and on the units used to measure time t = time, in days Find the substance's half-life, in days. Round your answer to the nearest tenth.

1. anonymous

2. anonymous

@puppylover52

3. puppylover52

srry idk this one

4. IrishBoy123

the equation is $\frac{N(t)}{N_o} = e^{-kt}$ set N /No to 1/2 and that is what half life means, the time for the amount to halve $\frac{1}{2} = e^{-0.1024T}$ take logs and solve for T, where t = T is the half life

5. Jack1

nice work @IrishBoy123 !

6. anonymous

so the answer cause I cant solve it?

7. anonymous

@IrishBoy123 @Jack1

8. anonymous

i solved for t and its still not it

9. Jack1

i think u use t to solve the 1/2 life... yeah?

10. Jack1

no, in irish's example: t is the half life

11. anonymous

can you find the answer @Jack1 ?

12. Jack1

yeah, i have the answer, what did u get for t?

13. anonymous

like 6.790

14. Jack1

yep, same here, exact answer for half life is t=6.76902 ish

15. Jack1

all i have is grams tho, i don't know the units of k, so i have no idea of the units of t or if k and t are both in the same units of measure...?

16. Jack1

(eg if k's relates to pounds/second or something and our No is in grams we have a problem)

17. anonymous

so you think you can solve it?

18. anonymous

@IrishBoy123

19. Jack1

lol... wat? so 6.8 isnt ur answer? (rounded to the nearest tenth)

20. anonymous

lol it is now my computer got messed up so it was saying everything incorrect thanks @Jack1

21. Jack1

ha. s'cool ;)