If 8 g of a radioactive substance are present initially and

If 8 g of a radioactive substance are present initially and 2 yr later only 4 g remain, how much of the substance will be present after 3 yr? After 3 yr there will be ? g of a radioactive substance.

Solution

Dear Student Thank you for using Chegg !! Given Initil quantty (Q0) = 8 g After 2 years Quantty (Q(t)) = 4 g Relation etween present quantity and future quantity for radioactive decay is Q(t) = Q0 e^-kt 8 = 4e^-2k 0.5 = e^-2k Taking natural log oth sides 0.693 = -2k k = -0.3465 Now to calculate quantity after 3 years Q(3) = 8e^-0.3465*3 = 2.829051628 g = 2.829 Solution