Question

Cobalt-60 has a half-life of 5 years. You are given a sample of 20 g of cobalt-60; how much will you have remaining after 10 years have passed?
10 g
20 g
5 g
15 g

Answer 1

Answer:

Option C, 5 gram

Explanation:

The half life of Cobalt-60 $= 5$ years

Given -

Sample of Cobalt-60 $= 20$ gram

Time of radioactive decay $= 10$ years

At the initial stage, when time T $= 0$ years, the mass of Cobalt-60 $= 20$ grams

when time T $= 5$ years, the mass of Cobalt-60

$= \frac{20}{2}\\ = 10$ grams

when time T $= 10$ years, the mass of Cobalt-60

$= \frac{10}{2}\\ = 5$ grams

Hence, option C is correct.

Answer 2

I believe it would be 5g, because after 5 years, that 20 grams would be down to 10 (reduced by half). With the remaining 10 grams, you would take half of that 10 to find how much remains after another half life goes by. I hope this helps you!