Question

Based on the graph, it can be concluded that the isotope which is most likely to be found with 6.25% of its original amount in 6 billion years is

Uranium-238
Thorium-235
Potassium-40
Rubidium-87

Answer 1

@thomaster

Answer 2

@genius12

Answer 3

@swissgirl

Answer 4

@amistre64

Answer 5

@dmezzullo

Answer 6

@kelliegirl33

Answer 7

Potassium-40. Do you know why? @watermelon14

Answer 8

no i don't know why I thought it was the first one. Why is is potassium-40 and thank very much!

Answer 9

You could use the half-life formula or JUST THINK ABOUT IT. The half life of Potassium-40 from what it looks like off the graph is like 1-1.5 bill years. If it halfs in 1-1.5 billion years, then there is 50% left. In another 1-1.5 billion years there will be 25%. If we do that 2 more times, we get 12.5% and then 6.25%. Our estimate is about 1-1.5 billion years hence repeating that about 4 times we get around 4-6 billion years for it to get to 6.25%. The rest obviously can't be an option because each of the other choices either reaches only 50% of its original amount in more than 6 billion years. The other option thats comes closest is U-238 which seems to have a half life of about 4 billion years. This means that at 8 billion years, it will be around at 25% the original amount. From this we can conclude the clear choice would have to be Potassium-40 since it comes the closest to remaining at 6.25% its original amount after approximately 6 billion years. @watermelon14

Answer 10

You get it?

Answer 11

yes! Thanks very much!!!!!! :3

Answer 12

Or use the formula:\[\bf A=A_0(0.5)^{\frac{t}{h}}\]If A = 6.25% then:\[\bf 0.0625=0.5^{\frac{6 \ BY}{h}} \implies \log(0.0625) = \frac{6 \ BY}{h}\log(0.5)\]\[\bf \implies h = half-life = \frac{6 \ BY(\log(0.5))}{\log(0.0625)} =1.5 \ BY\]This means that the substance has a half life of 1.5 billion years much like our estimate. Hence the only once it could be looking at the graph is Potassium-40. @watermelon14

Answer 13

and the 'BY' is billion years, and the "half - life" is simply "half life" not "half minus life". lol. @watermelon14 now i g2g. good luck.

Answer 14

okay!!! Thankssss!!!!!!!!!!!!