The tension of a rubber band in equilibrium is given by
$$
t=A T\left(\frac{x}{l_0}-\frac{l_0^2}{x^2}\right),
$$
where $t=$ tension, $T=$ absolute temperature, $x=$ length of the band, $l_0$ $=$ length of the band when $t=0, A=$ constant.
When $x$ is the constant length $l_0$, the thermal capacity $c_x(x, T)$ is observed to be a constant $K$.
(a) Find as functions of $T$ and $x$ :
(1) $\left(\frac{\partial E}{\partial x}\right)_T$ where $E=$ internal energy, (2) $\left(\frac{\partial c_x}{\partial x}\right)_T$, (3) $c_x(x, T)$, (4) $E(x, T)$, (5) $S(x, T)$, where $S=$ entropy.
(b) The band is stretched adiabatically from $x=l_0$ to $x=1.5 l_0$. Its initial temperature was $T_0$. What is its final temperature?