I have a ball out of plasticine thrown horizontally with speed $v$ on a steel ball that is attached from top to the ground on flexible straps in the middle (see picture). The mass of plasticine is $m$, mass of the steel ball is $M$. The straps have length $l$ in neutral position and affect potential energy while deflection $l^\prime> l$ with $P(l^\prime)=1/2\cdot k\cdot(l^\prime-l)^2$. The hit is completely inelastic.
What would be the total energy and total momentum look like before hit and after it?
What would be the maximum deflection d of the steel ball in dependence of $m$, $M$, $k$, $l$, $v$?
Would be thankful for answers!