I need to apply the Runge-Kutta of order 4 method for solving this equation
$$ y''(t)=\sum_{k=1}^{5} \frac{u_{k}(s_{k}-y(t))}{\|s_{k}-y(t)\|} $$
where $y'(0)=(\cos(\pi), \sin(\pi))$ and $y(0)=(0,0)$.
$u_k$ is a known vector with 5 components and $s_{k}$ is also a known vector with 2 components. How do I turn this into a system that I can apply Runge-Kutta of order $4$ to?