Question 14

Question

Video #5, Questions #1

The amount of time it takes for half of a sample to disappear is:

a
fission
b
half-life
c
nuclear chemistry
d
fusion
Question 15
Video #5, Question #2

The half-life for a 100-gram sample of radioactive element X is 5 days. How much of element X remains after 10 days have passed?

a
50 g
b
25 g
c
75 g
d
100 g
Question 16
Video #5, Question #3

Sodium-24 has a half-life of approximately 15 hours. If only one-eighth of the sodium-24 remains, about how much time has passed?

a
30 hours
b
15 hours
c
45 hours
d
60 hours

Answer 1

Here are the answers to the questions:

Question 14: The amount of time it takes for half of a sample to disappear is:

• b. half-life

Question 15: The half-life for a 100-gram sample of radioactive element X is 5 days. How much of element X remains after 10 days have passed?

• After 5 days, 50 g remains (first half-life).
• After another 5 days (10 days total), 25 g remains (second half-life).
• b. 25 g

Question 16: Sodium-24 has a half-life of approximately 15 hours. If only one-eighth of the sodium-24 remains, about how much time has passed?

• If one-eighth remains, that means 3 half-lives have passed (1 → 1/2 → 1/4 → 1/8).
• 3 half-lives at 15 hours each equals 45 hours.
• c. 45 hours