Thread: A couple of Exponential Functions Questions

8). The oldest rock knows to data found in Minnesota contains 2g of carbon 14(C^14). Using geological methods toestimate the original size of the rock, scentists estimate it to originally have contained 4.096kg of C^14 .The Half-life of c^14 is 5760 years.What is the approximate age of rock?

9). Land developers had to delay a housein development because the land had been previously used as a nucleur waste pit for Radium-D, an isotope has decayed to 1/√2 of its original. When could they build ifRadium-D has a half life of 22 years.

both use the y=ka^x, i just cant seem to get the answer right when i plugin the values its prol cuz i subed it in wrong,if some1 cud kindly help me it wud be apreciatted.

Originally Posted by usm_67

8). The oldest rock knows to data found in Minnesota contains 2g of carbon 14(C^14). Using geological methods toestimate the original size of the rock, scentists estimate it to originally have contained 4.096kg of C^14 .The Half-life of c^14 is 5760 years.What is the approximate age of rock?

9). Land developers had to delay a housein development because the land had been previously used as a nucleur waste pit for Radium-D, an isotope has decayed to 1/√2 of its original. When could they build ifRadium-D has a half life of 22 years.

both use the y=ka^x, i just cant seem to get the answer right when i plugin the values its prol cuz i subed it in wrong,if some1 cud kindly help me it wud be apreciatted.

The decay equation is indeed


How do we use this?

Well we know the half-life in each case, so what does that mean? It means that the when the time is equal to the half-life only half of the sample is left.

When t = 0


So k is the amount of sample initially, before it started to decay. So when t is equal to the half-life we only have (1/2)k of the substance:








So the decay equation is:


Try using this form for your questions. If you still have problems go ahead and let us know.

-Dan

well bro u totally lost me with the equation because he din teach us anythin like that, can u please solve it so the answer for first one is 63360 years and second one is 11 years

Originally Posted by usm_67

8). The oldest rock knows to data found in Minnesota contains 2g of carbon 14(C^14). Using geological methods toestimate the original size of the rock, scentists estimate it to originally have contained 4.096kg of C^14 .The Half-life of c^14 is 5760 years.What is the approximate age of rock?

Thus


Solve for t.

-Dan

what du u mean when u say t/5760 how wud i go by solvin that i get the rest of it

Originally Posted by usm_67

what du u mean when u say t/5760 how wud i go by solvin that i get the rest of it

You might want to find an English forum also.

lol my bad i was in a hurry, got the letters mixed up

someone please helpp.!!!!!!!!!!!!!!!!!!!i dont understand it

Originally Posted by topsquark

(I apparently left of the "-" in the exponent. Sorry about that!)









Now, the nice thing about this is that:



So the answer is 63360 years.

-Dan