Let's say there are two masses, attached together by a string, and there's a compressed spring in between them. When the string in between is cut off, the spring unloads, pushing both masses in opposite directions. My thinking: 1. Their momentums will be equal to each other. Their momentum before the string is cut is equal to zero (because they were not moving). So the sum of their final momentums should be also zero. 2. Their kinetic energies will be equal to each other. The spring unloads in both direction at equal rates, so I assume that their kinetic energies must also be equal. (I couldn't find a mathematical evidence in my Giancoli book to see if I am actually right) Are my conclusions right?