WAEC Physics 2022 Objective — Question 35
Question 35 of 50 from the West African Examinations Council (WAEC) Physics 2022 Objective paper, with the correct answer and a full explanation.
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The half-life of a radioactive substance is 15 hours. If at some instance, the sample has a mass of 512g, calculate the time it will take ⅞ of the sample to decay.
- A. 15 hours
- B. 30 hours
- C. 45 hoursCorrect
- D. 60 hours
Explanation
⅞ decayed means ⅛ remains. Number of half-lives for ⅛ to remain = 3 (since (½)³=⅛). Time = 3×15 = 45 hours.
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