4g of a radioactive material of half-life 10 days is spilled on a laboratory floor.
PHYSICS
JAMB 1991
4g of a radioactive material of half-life 10 days is spilled on a laboratory floor. How long would it take to disintegrate 3.5g of the material?
- A. 1\(\frac{1}{4}\) days
- B. 8\(\frac{1}{4}\) days
- C. 30 days
- D. 80 days
Correct Answer: C. 30 days
Explanation
half-life = 10 days
after 10 days, the 4g of element = 2g remaining with 2g disintegrated
after 10 days, 2g of element = 1g left with 1g disintegrated
hence, after 20 days, 3g of the element has been disintegrated with 1g left.
after 10 days, the 1g of element = 0.5g left with 0.5g disintegrated
after 30 days, we have 0.5g of element left with 3.5g disintegrated.
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