SPS SPS FM Pure 2021 May — Question 10

Exam BoardSPS
ModuleSPS FM Pure (SPS FM Pure)
Year2021
SessionMay
TopicFirst order differential equations (integrating factor)

10. A particular radioactive substance decays over time.
A scientist models the amount of substance, \(x\) grams, at time \(t\) hours by the differential equation $$\frac { \mathrm { d } x } { \mathrm {~d} t } + \frac { 1 } { 10 } x = \mathrm { e } ^ { - 0.1 t } \cos t$$
  1. Solve the differential equation to find the general solution for \(x\) in terms of \(t\). Initially there was 10 g of the substance.
  2. Find the particular solution of the differential equation.
  3. Find to 6 significant figures the amount of substance that would be predicted by the model at
    (a) 6 hours,
    (b) 6.25 hours.
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