1. A ball hanging on a pendulum hits an object standing on the table. The interaction is elastic and linear. After that, the object falls on the floor. 2. Relevant equations From state 1 to 2, we have the conservation of the potential energy of the pendulum to its kinetic energy, right before it hits the object. Then it is the kinetic energy conservation, so mv^2=mv1^2+mv2^2, right? 3. How to write the conservation laws of the next states?