Rankers Physics

Nucleus: Practice Problem & Solution

The half life of radium is about 1600 years. Out of 100 g of radium existing now, 25 g will remain undecayed after: (2004)
6400 years
2400 years
3200 years
4800 years

Solution Explained:

To solve this problem, we apply the core principles of Nucleus. Understanding the underlying formula is key to arriving at the correct answer below:

The fraction remaining is $25/100 = 1/4 = (1/2)^2$. This means 2 half-lives have passed. The time elapsed is $2 \times 1600 = 3200$ years.

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