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Q30E

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Linear Algebra With Applications
Found in: Page 415
Linear Algebra With Applications

Linear Algebra With Applications

Book edition 5th
Author(s) Otto Bretscher
Pages 442 pages
ISBN 9780321796974

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Short Answer

The temperature of a hot cup of coffee can be modelled by the DE

T'(t)=-k(T(t)-A)

(a) What is the significance of the constants K and A?

(b) Solve the DE for T (t) in terms of K, A and the initial temperature T0

(a) If the constant A is positive then the temperature of the hot cup of coffee modelled by the DE is positive and A is negative then the temperature of the hot cup of coffee modelled by the DE is negative.

(b)The solution is A=T0-Ce-kt

See the step by step solution

Step by Step Solution

Step 1 Explanation for Linear Differential operators and linear differential equations

A transformation T from C to Cto of the form role="math" localid="1660801324664" T(f)=f(n)+an-1f(n-1)+...+a1f'+a0fis called an nth-order linear differential operator.Here f(k)denote the k-th derivative of function f and the coefficients akare complex scalars.

If T is an nth-order linear differential operator and g is a smooth function, then the equation becomes

T(f)=g

(or)

f(n)+an-1f(n-1)+...+a1f'+a0f=g

Is called an nth-order linear differential equation (DE).The DE is called homogeneous if g = 0 and inhomogeneous otherwise.

(a) Step 2: Explanation of the significance for the constants K and A

Consider the temperature of a hot cup of coffee can be modelled by the DE

T'(t)=k(T(t)-A)

Here k and A be the constants in the differential equation.

The constant is called the continuous growth rate if it is positive and the continuous decay rate if it is negative.

If the constant A is positive then the temperature of the hot cup of coffee modelled by the DE is positive and A is negative then the temperature of the hot cup of coffee modelled by the DE is negative.

Since both the constants k and A be the significant terms in the temperature of the hot cup of coffee modelled by the DE

(b) Step 3 : Solution for the DE for T(t) in terms k, A and the initial temperature T0

Consider the temperature of a hot cup of coffee can be modelled by the DE

T'(t)=k(T(t)-A)

Here k and A be the constants in the differential equation.

T'(t)=k(T(t)-A)T'(t)=-k(T(t))+kAT'(t)=(A-t)k T'(t)=dTdtdTdt=(A-T)kdTdt=-k(T-A)

Integrating on both sides we get,

dTdt=-k(T-A)dT(T-A)=-kdt dT(T-A)=-kdtlnT-A=-kt+CT-A=e-ktecT-A=Ce-ktT(t)=A+Ce-kt A=T-Ce-kt

Here initial temperature becomes T0and the solution is A=T0-Ce-kt.

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