An accident in a research laboratory released a quantity of the radioactive isotope cobalt-60. Twenty-one years after the accident, the quantity of cobalt-60 present will be 6.25% of its original level.
What is the half-life of cobalt-60?
4.20 years4.20\text{ years}4.20 years
5.25 years5.25\text{ years}5.25 years
7.00 years7.00\text{ years}7.00 years
10.5 years10.5\text{ years}10.5 years
144 exam-style questions on CIE IGCSE Physics 5.2.4a Half-life. Each one has a worked solution and a mark scheme showing where the marks go.