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Thanks Alna, for your answer! Yes, I'm sorry for the mistake, I just didn't notice it, it's actually :h=-T(dv/dT) at constant p.

Here's my answer for this question: 

\(H=U+pv\)(H is the enthalpy)

\(H=Q+W+pv\)(U=Q+W)

\(dH=dQ+dW+d(pv)\)

knowing that \(dQ={C}_{v}dT+hdp\)

\(dH={C}_{v}dT+hdp-pdv+pdv+vdp\)

\(dH={C}_{v}dT+hdp+vdp\)

\(dH={C}_{v}dT+(h+v)dp\)

H is a state function, that means it's a total  differential:

\(\begin{pmatrix} \frac{\partial{C}_{v}} {\partial p} \end{pmatrix}_{T}=\begin{pmatrix} \frac{\partial({h+v})} {\partial T} \end{pmatrix}_{p} \)

\(\begin{pmatrix} \frac{\partial{C}_{v}} {\partial p} \end{pmatrix}_{T} =\begin{pmatrix} \frac{\partial{h}} {\partial T} \end{pmatrix}_{p} + \begin{pmatrix} \frac{\partial{v}} {\partial T} \end{pmatrix}_{p} \)(1)

On the other hand we have:

\(dQ={C}_{v}dT+hdp\)\(*(\frac{1}{T})\)

\(dS=\frac{{C}_{v}}{T}dT+\frac{h}{T}dp\)

S is a state function, that means it's a total  differential:

\(\begin{pmatrix} \frac{\partial({C}_{v}/T)} {\partial p} \end{pmatrix}_{T} = \begin{pmatrix} \frac{\partial({h/T})} {\partial T} \end{pmatrix}_{p}\)

\(\frac{1}{T}\begin{pmatrix} \frac{\partial{C}_{v}} {\partial p} \end{pmatrix}_{T} = \frac{ {T} \begin{pmatrix} \frac{\partial{h}} {\partial T} \end{pmatrix}_{p} - \frac{h}{T²}}{T²}\)

\(\begin{pmatrix} \frac{\partial{C}_{v}} {\partial p} \end{pmatrix}_{T} = \begin{pmatrix} \frac{\partial{h}} {\partial T} \end{pmatrix}_{p} -\frac{h}{T}\)(2)

(1)=(2)

\(\begin{pmatrix} \frac{\partial{h}} {\partial T} \end{pmatrix}_{p} + \begin{pmatrix} \frac{\partial{v}} {\partial T} \end{pmatrix}_{p} = \begin{pmatrix} \frac{\partial{h}} {\partial T} \end{pmatrix}_{p} - \frac{h}{T}\)

 

\( \begin{pmatrix} \frac{\partial{v}} {\partial T} \end{pmatrix}_{p} = - \frac{h}{T}\)

 

\(h= -T\begin{pmatrix} \frac{\partial{v}} {\partial T} \end{pmatrix}_{p} \)

.
Jan 15, 2017
 #1
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Take the integral:
 integral u^2 sqrt(a^2 - u^2) du
For the integrand u^2 sqrt(a^2 - u^2), (assuming all variables are positive) substitute u = a sin(u) and du = a cos(u) du. Then sqrt(a^2 - u^2) = sqrt(a^2 - a^2 sin^2(u)) = a cos(u) and u = sin^(-1)(u/a):
 = a integral a^3 sin^2(u) cos^2(u) du
Factor out constants:
 = a^4 integral sin^2(u) cos^2(u) du
Write cos^2(u) as 1 - sin^2(u):
 = a^4 integral sin^2(u) (1 - sin^2(u)) du
Expanding the integrand sin^2(u) (1 - sin^2(u)) gives sin^2(u) - sin^4(u):
 = a^4 integral(sin^2(u) - sin^4(u)) du
Integrate the sum term by term and factor out constants:
 = -a^4 integral sin^4(u) du + a^4 integral sin^2(u) du
Use the reduction formula, integral sin^m(u) du = -(cos(u) sin^(m - 1)(u))/m + (m - 1)/m integral sin^(-2 + m)(u) du, where m = 4:
 = 1/4 a^4 sin^3(u) cos(u) + a^4/4 integral sin^2(u) du
Write sin^2(u) as 1/2 - 1/2 cos(2 u):
 = 1/4 a^4 sin^3(u) cos(u) + a^4/4 integral(1/2 - 1/2 cos(2 u)) du
Integrate the sum term by term and factor out constants:
 = 1/4 a^4 sin^3(u) cos(u) - a^4/8 integral cos(2 u) du + a^4/8 integral1 du
For the integrand cos(2 u), substitute s = 2 u and ds = 2 du:
 = 1/4 a^4 sin^3(u) cos(u) - a^4/16 integral cos(s) ds + a^4/8 integral1 du
The integral of cos(s) is sin(s):
 = -1/16 a^4 sin(s) + 1/4 a^4 sin^3(u) cos(u) + a^4/8 integral1 du
The integral of 1 is u:
 = -1/16 a^4 sin(s) + (a^4 u)/8 + 1/4 a^4 sin^3(u) cos(u) + constant
Substitute back for s = 2 u:
 = (a^4 u)/8 - 1/16 a^4 sin(2 u) + 1/4 a^4 sin^3(u) cos(u) + constant
Apply the double angle formula sin(2 u) = 2 sin(u) cos(u):
 = (a^4 u)/8 + 1/4 a^4 sin^3(u) cos(u) - 1/8 a^4 sin(u) cos(u) + constant
Express cos(u) in terms of sin(u) using cos^2(u) = 1 - sin^2(u):
 = (a^4 u)/8 - 1/8 a^4 sin(u) sqrt(1 - sin^2(u)) + 1/4 a^4 sin^3(u) cos(u) + constant
Substitute back for u = sin^(-1)(u/a):
 = 1/8 a^4 sin^(-1)(u/a) + 1/4 u^3 sqrt(a^2 - u^2) - 1/8 a^3 u sqrt(1 - u^2/a^2) + constant
Factor the answer a different way:
 = 1/8 (a^4 sin^(-1)(u/a) + 2 u^3 sqrt(a^2 - u^2) - a^3 u sqrt(1 - u^2/a^2)) + constant
Which is equivalent for restricted u and a values to:
Answer: |= 1/8 (u sqrt(a^2 - u^2) (2 u^2 - a^2) + a^4 tan^(-1)(u/sqrt(a^2 - u^2))) + constant

Jan 15, 2017

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