Water is being heated in a kettle. At time t seconds, the temperature of the water is θ∘C. The rate of increase of the temperature of the water at time t is modelled by the differential equationdtdθ=λ(120−θ)θ≤100where λ is a positive constant. Given that θ=20 when t=0(a) solve this differential equation to show thatθ=120−100e−λt(8)
Q. Water is being heated in a kettle. At time t seconds, the temperature of the water is θ∘C. The rate of increase of the temperature of the water at time t is modelled by the differential equationdtdθ=λ(120−θ)θ≤100where λ is a positive constant. Given that θ=20 when t=0(a) solve this differential equation to show thatθ=120−100e−λt(8)
Identify Given Equation: Identify the given differential equation and the initial condition. The differential equation is given by dtdθ=λ(120−θ), and the initial condition is θ=20 when t=0.
Separate Variables: Separate the variables θ and t in the differential equation.We can rewrite the equation as 120−θdθ=λdt.
Integrate Both Sides: Integrate both sides of the equation with respect to their respective variables.The integral of 120−θdθ with respect to θ is −ln∣120−θ∣, and the integral of λdt with respect to t is λt. We add the constant of integration C on the right side.
Solve for Constant: Solve for the constant of integration using the initial condition.When t=0, θ=20. Plugging these values into the integrated equation gives us −ln∣120−20∣=λ⋅0+C, which simplifies to −ln(100)=C.
Express Constant in Terms: Express the constant C in terms of the initial condition.C=−ln(100).
Substitute Value of C: Substitute the value of C back into the integrated equation.−ln∣120−θ∣=λt−ln(100).
Simplify by Exponentiating: Simplify the equation by exponentiating both sides to remove the natural logarithm. e(−ln∣120−θ∣)=e(λt−ln(100)), which simplifies to ∣120−θ∣=100e(−λt).
Solve for Theta: Solve for theta by removing the absolute value, considering that θ≤100. Since theta is always less than or equal to 100, we have 120−θ=100e(−λt).
Isolate Theta: Isolate theta to find the temperature as a function of time. θ=120−100e−λt.