Past exam of the mathematics course of the University of Cambridge / 2026 / iii / Paper 352 / 2 / c / ii / Solution

As $\dot{ϵ}\to 0$, $a\to 0$, $F\to 1$, andThe Trouton ratio is therefore three. This is also the small-rate Oldroyd-B result because finite extensibility is irrelevant while polymer deformation remains small.