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1.11.7 Differential equations with separable variables (A-level only)

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Question 1
a.

The mass MMM grams of a crystal growing in a chemical bath at time ttt hours is modelled by the differential equation

dMdt=10tMe2t,M≥0,t≥0 \frac{\text{d}M}{\text{d}t} = \frac{10t \sqrt{M}}{\text{e}^{2t}}, \quad M \ge 0, \quad t \ge 0 dtdM​=e2t10tM​​,M≥0,t≥0

Given that the initial mass of the crystal is 444 g, solve this differential equation to find an expression for M12M^{\frac{1}{2}}M21​ in the form M12=f(t)M^{\frac{1}{2}} = f(t)M21​=f(t).

[6]
b.

Hence determine the equation of the horizontal asymptote to the curve with equation M12=f(t)M^{\frac{1}{2}} = f(t)M21​=f(t).

[2]

1.11.7 Differential equations with separable variables (A-level only) Questions

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