Solution

ID: past-exam-of-the-differential-equations-1-course-of-the-university-of-oxford/2017/2/b/iv/solution

For each departure time , define
Each branch satisfies the ordinary differential equation, and both joins have matching value and matching derivative zero. Thus is continuously differentiable and satisfies the same initial value problem. If , the solutions differ on , proving infinitely many solutions on every with .
The uniqueness hypotheses fail when the solution reaches . Indeed
No finite Lipschitz constant works on a rectangle containing that level in its interior. The local theorem still controls the earlier branch near zero; it cannot be extended through a point where its hypotheses fail. These are waiting-time continuations at a non-Lipschitz equilibrium.
Figure 1.
The same initial solution admits different departure times from a non-Lipschitz equilibrium
. Each curve arrives at at time two, may remain there, and then decreases again. All displayed joins are continuously differentiable. Details.

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