Solution
= Solution
The <Maxwell model> has a spring of modulus $G_0$ in series with a <dashpot> of <viscosity> $\eta$. Their stresses are equal and strains add, giving $\dot\gamma=\dot\sigma/G_0+\sigma/\eta$. After a step <strain> $\gamma_0$, the <strain> rate is zero for $t>0$, so $\dot\sigma=-\sigma/\tau$ with $\tau=\eta/G_0$. Initially the spring takes the step, $\sigma(0^+)=G_0\gamma_0$. Hence
$$
\boxed{G(t)=G_0e^{-t/\tau},\qquad\tau=\eta/G_0.}
$$