WAEC Physics 2021 Objective — Question 38
Question 38 of 50 from the West African Examinations Council (WAEC) Physics 2021 Objective paper, with the correct answer and a full explanation.
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38. A radioactive material has a half-life of 1.0 hour. If 200.0 g of it was present at 6 a.m. on a certain day, how many grams will have decayed by 9 a.m. on the same day?
- A. 175.0 gCorrect
- B. 150.0 g
- C. 100.0 g
- D. 187.5 g
Explanation
From 6 a.m. to 9 a.m. is 3 hours = 3 half-lives. 200→100→50→25 g remaining. Decayed = 200-25 = 175.0 g.
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