Question

Cobalt-60 can be used by scientists for the purpose of radioactive dating. Cobalt-60 has a half-life of 5,272 years. A fossilized rock originally contained 25 grams of Co-60. When tested, the rock only contains 6.25 grams of Co-60. Approximately how old is the item?

Answer 1

Answer:10,500

Explanation: Im doing it now. I got it wrong and they said the correct answer is C: 10,500

Answer 2

Answer:

The rock is 10,544 years old.

Explanation:

The half-life is the time that a mass of a compound decays by half. It means that at every 5,272 years, the mass of Cobalt-60 will be reduced by half. The mass after n half-lives can be calculated by:

$m = \frac{m_{0}}{2^n}$

Where $m_{0}$ is the initial mass.

6.25 = 25/2ⁿ

2ⁿ = 25/6.25

2ⁿ = 4

2ⁿ = 2²

n = 2 half-lifes

The time passed is

t = half-life * n

t = 5,272*2

t = 10,544 years.

The rock is 10,544 years old.