Question

Suppose that the half-life of a certain substance is 14 minutes. At 9:30 a.m., 500 mg of the substance is present. How many milligrams of the substance has decayed by 10:05 a.m.?

A) 125 mg
B) 250 mg
C) 375 mg
D) 500 mg

Answer 1

The substance will have completely decayed by 10:05 a.m.

Step-by-step explanation:

The half-life of a substance is the time it takes for half of the substance to decay or break down. In this case, the half-life of the substance is 14 minutes. So, let's calculate the number of half-lives from 9:30 a.m. to 10:05 a.m.:

1. 9:30 a.m. is the starting time, and 10:05 a.m. is 35 minutes later.
2. 35 minutes divided by 14 minutes (the half-life) is approximately 2.5.
3. Since we cannot have half of a half-life, we round down to 2 half-lives.

Each half-life represents a 50% decay of the substance. So, after 2 half-lives, the substance would have decayed by 100% or completely. Therefore, the answer is D) 500 mg, as all of the substance has decayed by 10:05 a.m.