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
Verified Correct Answer: C.
Physical Principles & Numerical Solution
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.
Source: Myschool Past Questions Archive (Record #28207)