QCEVault

Differential equations — Question 82

Original QCE Vault practice · 6 marks

Q82 · Practice questionComplex familiar6 marks

QUESTION 82 (6 marks)

A radioactive sample initially has mass 120 mg120\ \mathrm{mg}. After 8 days its mass is 90 mg90\ \mathrm{mg}. Assume exponential decay.
a)
Determine a model m(t)=120e−ktm(t)=120e^{-kt}.
[2 marks]
b)
Determine the half-life.
[2 marks]
c)
Determine when the mass first falls below 20 mg20\ \mathrm{mg}.
[2 marks]
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