In a bad late-night science fiction film, a villain is using a large collection of rare radioactive atoms as energy for a weapon to threaten the good guys. The atoms have a half-life of 1 hour. The villain has 4 kilograms of the radioactive material now, and he needs a minimum of 1 kg. for his weapon to work. After how much time will the weapon no longer be a threat?
A) just a little after 1 hr
B) just a little after 2 hrs
C) just a little after 4 hours
D) just a little after 16 hours
E) can't be determined from the information given

Question

Quizplus · Accepted Answer

The half-life of the radioactive material is 1 hour, meaning the amount of material halves every hour. Starting with 4 kg, after 1 hour it would be 2 kg, and after 2 hours it would be 1 kg. Just after 2 hours, the amount would drop below 1 kg, making the weapon no longer a threat.

In a Bad Late-Night Science Fiction Film, a Villain Is