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1.9.31 Formulate first order differential equations (A-level only)

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Question 26

A high-performance server processor is equipped with a failsafe cooling system. When the system is shut down at time t=0t = 0t=0 minutes, the processor temperature, θ∘C\theta^\circ\text{C}θ∘C, decreases at a rate proportional to the difference between the processor's current temperature and the ambient room temperature, which is a constant 25∘C25^\circ\text{C}25∘C.

Immediately upon shutdown, the processor is at 145∘C145^\circ\text{C}145∘C and its temperature is decreasing at a rate of 3∘C3^\circ\text{C}3∘C per minute.

a.

Show that

dθdt=−0.025(θ−25) \frac{d\theta}{dt} = -0.025(\theta - 25) dtdθ​=−0.025(θ−25)
[3]
b.

Solve the differential equation

dθdt=−0.025(θ−25) \frac{d\theta}{dt} = -0.025(\theta - 25) dtdθ​=−0.025(θ−25)

to find an expression for θ\thetaθ in terms of ttt.

[4]
c.

Determine the time taken for the processor temperature to drop to 85∘C85^\circ\text{C}85∘C. Give your answer to the nearest minute.

[3]

1.9.31 Formulate first order differential equations (A-level only) Questions

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