Question

A radioactive element has a half-life of 2,000 years. If a sample of this
element begins with a mass of 100 grams, how long would you have to waitfor the mass to decrease to 25 grams?
A. 4,000 years
B. 8,000 years
C. 500 years
D. 2,000 years

Answer 1

Answer:

A = 4000 years

Explanation:

Given data:

Half life = 2000 years

Total mass = 100 g

Mass remain = 25 g

Time taken to reduces to 25 g = ?

Solution:

At time zero = 100 g

At first half life = 100 g/2 = 50 g

At 2nd half life = 50 g / 2 = 25 g

Time taken:

Half life = Time elapsed / number of half lives

2000 years = Time elapsed / 2

Time elapsed = 2000 years × 2

Time elapsed = 4000 years