Solution (source code)

= Solution

For equal point masses at $1/2$ and $3/2$ with $h_0=\theta$,
$$
\bar h(t)=\frac\theta2
\frac{e^{-\theta t/2}+3e^{-3\theta t/2}}
{e^{-\theta t/2}+e^{-3\theta t/2}}.
$$
Its initial value is $\theta$ because $\mathbb EU=1$, while $\bar h(t)\to\theta/2$ as the more frail survivors are progressively depleted.